Call of Cthulhu 7e Cthulhu Mythos Guide: Cultists, Monsters, and Gods

Introduction

The Cthulhu Mythos is not a bestiary to empty into an encounter. It is the name investigators give to evidence that the world is larger, older, and less human-centered than they believed. A creature in a cellar, an impossible artifact, a cult's ritual language, and a star no map includes can all point toward that conclusion without the Keeper explaining everything.

For a Keeper, Mythos material works when it changes the investigation. An entity leaves a trace, creates a pattern, wants something, distorts a relationship, or makes an ordinary solution inadequate. Investigators need enough evidence to make an informed decision before delay becomes costly, well short of a complete cosmic taxonomy.

This guide covers the whole Mythos toolkit in the order you are likely to need it: how to use the Mythos in a scenario, cultists, monsters and their statistics (including Deep Ones, Mi-Go, and Shoggoths), Great Old Ones, Outer Gods, and Keeper advice that ties them together. Rules details are checked against the Keeper Rulebook's monster and deity chapter; for full stat blocks, use the book.

Hot Take

The most useful Mythos entity in the Keeper Rulebook is the human cultist, and most Keepers reach for the god first.

The rulebook admits why so many scenarios use cultists, Deep Ones, Mi-Go, and ghouls: they are roughly human-scale, so investigators can question, follow, bribe, fight, or outrun them. A god gives you one scene of awe. A landlord, a doctor, and a frightened treasurer who serve that god give you a whole investigation. Start with the people and let the entity stay mostly offstage. When the investigators finally glimpse what the cult serves, they will already know what it has cost.

How to Use the Cthulhu Mythos

What the Mythos Does in a Scenario

The Mythos is most useful as a force that makes normal assumptions fail. A locked door does not guarantee privacy. A family resemblance does not prove a family relationship. A faithful record can show an event that no possible witness could have seen. Each violation should point back into the investigation.

Before choosing a particular entity or god, write the scenario effect in plain language:

• People are being changed by something they think is medicine.
• A coastal community protects a secret that keeps the sea from taking more than it already has.
• An artifact lets people find each other in dreams, and someone uses that access to recruit them.
• A scientific project has made contact with a pattern it cannot stop interpreting.
• A family has confused survival with loyalty to the thing that saved their ancestor.

The effect gives you a mystery with human consequences. The Mythos supplies the alien cause, sensory evidence, and reason ordinary explanations eventually stop working. If you begin with a favorite creature instead, ask what changes in a town, household, institution, or body because it exists nearby.

Keep the scale honest. A local case can remain local. Not every ritual is the first move in an apocalypse. A disappearing dockworker, contaminated well, or compromised professor can be frightening because investigators can still imagine containing the harm. Save world-ending implications for a campaign that has earned them.

Choose an Encounter Role Before an Entity

An entity's most important property is what it does at the table. Choose that job before its appearance or mechanics. This keeps encounters from collapsing into sighting, roll, and fight.

One entity can fill several roles across an arc. A trace becomes a predator when investigators enter its territory. A messenger becomes a rival after it recognizes what they carry. Do not reveal every role at once. Let conclusions change as evidence changes.

The role also tells you how much mechanical detail to prepare. A trace may need no statistics. A custodian might need only the procedures relevant if investigators challenge it. A catastrophe may require an evacuation map, a clock, and several human NPCs before it needs combat rules.

Present the Unknown in Layers

Do not lead with a complete visual description. The Keeper Rulebook tells Keepers not to portray Mythos monsters only through sight: smell, sound, and the otherworldly atmosphere around them matter too. A list of tentacles and teeth becomes familiar quickly. Signals that investigators can compare and interpret stay unsettling.

1. Ordinary disruption. Start with something a reasonable person might explain away: an animal refuses to enter a building, patients develop the same symptom, a manifest lists a repeated impossible weight, or a local family stops appearing in public.
2. Sensory contradiction. Add a sound, smell, texture, temperature, rhythm, or visual inconsistency. A basement smells like brine far from the coast. A recording contains a pulse no microphone should capture. Mud on a car comes from a place no road reaches.
3. Human cost. Show who pays. Someone loses sleep, hides a changed relative, takes dangerous work, lies to protect a community, or becomes a target because they know too much. Human cost keeps the supernatural from becoming wallpaper.
4. Direct contact. Only then show the entity, manifestation, or full consequence. A creature in a tunnel is frightening; a creature connected to missing workers, altered soil, and decades of denials is a decision point.

Each layer should answer a question while opening a more disturbing one. The players should be able to say, "We now know the water is involved," before they must learn why.

Build Clues Around Consequences

The entity itself is rarely the only clue. Its needs, habits, victims, followers, food source, tools, boundaries, and aftermath produce evidence. Build clues around those consequences so the investigation continues when the creature remains unseen.

Prepare several routes to each essential conclusion. The group might find residue, interview a cleaner, compare shipping records, or follow a frightened worker. A missed roll, stubborn NPC, or destroyed document should change the route, not erase the mystery. The scenario design guide covers resilient investigation structures.

Separate a clue from its interpretation. "The cult serves a sea entity" is an interpretation. Wet footprints ending at a sealed wall, payments to divers, and a recurring phrase in old letters are clues. Let players build the conclusion. When they form the wrong theory, provide evidence that challenges it rather than correcting them from behind the screen.

Give Alien Things Goals, Not Human Morality

Mythos entities should have objectives, but should not behave like humans wearing monster masks. A goal is a pattern of action that produces observable consequences, not an emotional motive investigators can easily understand.

A being may gather material, protect offspring, return to a place, obey a distant master, maintain a boundary, conduct an experiment, seek a human quality, or escape a greater danger. These objectives can be comprehensible without making the entity sympathetic or predictable. The rulebook makes the same point about intelligence: many monsters are as smart as the investigators or smarter, will not automatically seek combat, and may take captives as slaves, sacrifices, or experimental subjects instead of killing them.

Constraints are not always weaknesses. They can be priorities, habits, environmental limits, divided attention, or a need for intermediaries. Their purpose is to give investigators a way to make plans. A threat with no observable limit is not more cosmic. It is just harder to run fairly.

For cultists, collaborators, and compromised witnesses, use human motives as well as alien pressure. A person may cooperate for survival, curiosity, money, grief, ideology, or belonging. The Cultists section below builds those people in detail, and the NPC creation guide helps make them more than guards waiting for a fight.

Use Escalation Investigators Can See

The Mythos becomes threatening when it acts, not when the Keeper silently decides it is stronger. Build visible changes. Each step should create evidence, increase a cost, or close an option while opening another.

Reveal escalation through the fiction: a missing person becomes public, a place becomes unsafe, an ally stops answering, or a reliable record changes. A visible clock lets players make informed choices. It should not punish them for discussing evidence or taking reasonable care.

Every stage should create a new lead as well as greater risk. A flooded archive may reveal a sealed room. A mass dream may endanger witnesses but give the group a shared map. Quiet escalation is often stronger than loud escalation: a cult that gains legal control of a building, a family that moves a relative away, or an artifact appearing in unrelated auctions all show the situation advancing without providing a target to shoot. Each entity type below gets its own version of this track, because cults escalate through commitment, Mi-Go through extraction, Shoggoths through spread, and gods through the systems they bend.

Change the Familiar World

Start with a place whose routines investigators understand: a dock, hospital ward, rural road, museum, boarding house, office, school, cemetery, or church hall. Then change one thing at a time.

Ask what the force changes about the place's ordinary function. A hospital has a wing no staff member admits exists, but bills keep being issued for it. A museum storage system is accurate except for a collection that appears in every catalog without a physical location. A wharf's tide schedule is correct, yet workers return wet from a shift when the water was miles away.

Use sensory details with restraint. A repeated sound, smell, color, or sensation should become more meaningful as the group learns. The scent of iodine might first imply a hospital, then recur at an inland crime scene, then identify a collaborator. The horror atmosphere guide offers further tools for making familiar places wrong.

Cultists

Cultists are the human face of an inhuman problem. They rent rooms, recruit neighbors, hide records, misread signs, keep secrets from one another, and decide what they will do for a promise of belonging, power, safety, knowledge, or transcendence. That makes them far more useful than a room full of interchangeable opponents waiting for investigators to arrive.

The Keeper Rulebook's scenario advice explains why they exist: many Mythos beings are too powerful to defeat and too horrific to know directly, so human followers let a story reveal their gods "in a diluted form" and let investigators win small victories without dying every week. The same chapter warns against infallible NPCs and says plainly that cultists are only human, so let them make human mistakes.

The worst thing a cult can do is not a hooded ceremony. It is the moment investigators realize the people they trusted have been quietly making ordinary life easier for the cult for years. The landlord who offers access to the basement, the doctor who alters a report, the editor who kills a story, the charity organizer who learns who is vulnerable, and the sibling who asks a victim to stop asking questions are all more frightening than a masked stranger.

Cultists Are a Human System

Treat a cult as an organization with a stated purpose, an actual purpose, a public face, internal roles, and weak points. It may be a religious group, a lodge, a salon, a research circle, a mutual-aid society, a business network, a criminal operation, or a small group held together by a charismatic person. Its members do not need to call themselves cultists. The rulebook notes that real Mythos cults often hide behind a benign facade, with only the inner circle aware of the true purpose.

The stated purpose should not be a joke. A group that offers food, employment contacts, grief support, or a place to belong may provide real help while also steering people toward something dangerous. That contradiction creates better scenes than a group that is obviously sinister from its first appearance.

Keep the actual Mythos connection partly outside the organization. A leader may believe they understand it, while ordinary members only know rules, taboos, and tasks. This lets investigators dismantle a local operation without pretending they have solved the cosmic threat behind it.

Start With a Human Harm

Open with a specific person or institution damaged by the cult's activity. A missing-person report, workplace accident, coerced confession, suspicious death, altered inheritance, closed newspaper story, vanished research file, or sudden change in a loved one creates a reason to investigate before the group knows the word "cult."

1. Visible harm: Someone has been hurt, disappeared, discredited, pressured, or cut off from support.
2. Social pattern: Several people repeat a phrase, protect the same institution, or redirect questions toward a trusted figure.
3. Operational proof: Records, payments, keys, schedules, meeting locations, or a compromised official show the group has structure.
4. Committed act: The investigators learn what is about to happen and what will be lost if no one intervenes.

Every stage needs multiple clue routes. A missing member can be found through family, work, bank records, a landlord, public notices, old correspondence, or a former friend. Do not make one secret password or one locked diary the only way into the plot.

Make the initial harm personal but not automatically fatal. A witness who is frightened, ashamed, indebted, or treated as unreliable gives the group someone to protect and an early choice about how publicly to act.

Build a Cult That Can Be Investigated

Write a small organization map before writing any ritual or confrontation. Players can investigate people, routines, property, money, records, and relationships. They cannot investigate an abstract evil symbol.

Give each layer a human caretaker. The public speaker may have no access to the books. The treasurer may fear the leader but understand the money. A courier may know routes without understanding what they carry. A relative may be close to a key member but excluded from meetings. This spread gives investigators ways to progress through observation, persuasion, stealth, pressure, and compassion.

Give each caretaker a goal, fear, resource, limitation, and change trigger. A cult does not need a dozen fully detailed members. Four or five people with different degrees of knowledge will produce more playable scenes than a list of names.

Use Recruitment and Belonging

Recruitment is how the cult enters the investigators' world. A member may invite someone after a bereavement, a financial setback, an academic disappointment, a family conflict, a legal problem, or a frightening encounter that ordinary institutions dismiss. The offer can be manipulative and still answer a real unmet need.

Do not frame every recruit as foolish. The group may have offered help when no one else did. Investigators become more compelling when they can offer safety, evidence, or a way to leave instead of only condemnation, and social investigators get a real job in a scenario that might otherwise become a raid.

Recruitment leaves practical evidence: invitation lists, transportation arrangements, donations, private letters, altered routines, borrowed rooms, missing work shifts, and people who suddenly avoid old friends. Those details turn atmosphere into leads.

Create Ranks, Fractures, and Mistakes

Cultists miscommunicate, protect themselves, compete for recognition, lose nerve, underestimate investigators, and disagree about how much harm the group should cause. Those failures are the human consequences of secrecy and pressure, and the rulebook suggests they can confound players who look for a rationale behind a cultist's mistaken behavior.

Use fractures to create options rather than a single betrayal scene. An organizer might redirect investigators to protect themselves. A recruiter might warn a victim without becoming an ally. An enforcer might become dangerous when a loved one is threatened. A devotee might cause a public disruption that exposes the group at the worst possible moment.

Let mistakes leave traces: a meeting runs late, a payment is duplicated, an invitation goes to the wrong person, a guard abandons a post, or two members contradict each other about where someone went. Human error is both a clue source and a reminder that the group is not a hive mind.

Plan Clues Beyond the Hidden Temple

The cult's final meeting place is usually the least useful place to begin. Investigators should find the group through its effects on ordinary life, then decide whether infiltration, exposure, surveillance, rescue, or direct action is the best response.

For every essential conclusion, prepare at least three ways to reach it. If the group needs to learn where a meeting is held, they might follow a member, question a former recruit, examine a payment record, find a transportation pattern, or overhear an internal argument. This protects the investigation from one failed roll and respects unconventional player approaches.

Give Infiltration a Real Cost

Infiltration works when joining, pretending to join, or attending a public event asks investigators to compromise something: time, reputation, safety, a relationship, or their ability to act openly afterward. The point is to make access valuable enough that the group must decide how much risk to accept, not to force a disguise scene.

Before an infiltration scene, establish four facts:

1. What behavior earns trust here?
2. What question would expose an outsider?
3. What evidence can the group obtain if they succeed?
4. What happens if the cult suspects them but cannot prove anything?

The last question matters. Immediate capture is often less interesting than surveillance, blackmail, social isolation, a false accusation, or pressure on someone the investigators care about. These consequences keep the cult active in the wider world and make a partial success feel consequential.

Let players choose their own entry point. A journalist may attend openly, a doctor may follow a patient, a criminal may approach the supply chain, and an academic may offer expertise. The most effective plan often uses two approaches at once: one investigator gains access while another follows the organization outside the meeting room.

Escalate Through Commitment

Cult escalation should track the group's increasing commitment, not only the number of enemies in a scene. Each step should demand more secrecy, sacrifice, or complicity from members and create more danger for people who want to leave.

Make the clock legible. A meeting date, property closing, scheduled transport, anniversary, legal hearing, public event, or missing person's deadline tells the players why they must act.

Cultist Scenario Patterns

Use different social structures to avoid repeating the same basement-ceremony story. The Mythos element can stay distant while the human organization drives the case.

The rulebook's deity entries supply real-world-flavored cult hooks for these patterns: the Esoteric Order of Dagon operating openly in New England seaports, the Brotherhood of the Black Pharaoh and other cults devoted to Nyarlathotep's masks, and the Brothers of the Yellow Sign among Hastur's worshipers. For a one-shot, put the committed act on a short, visible schedule and make the target a person the investigators can reach. For a campaign, let the group stop one cell while records, an escaped leader, a compromised institution, or a former recruit points toward a larger network.

Cultists in a Fight

Direct contact with cultists should show the organization reacting to pressure. A confrontation can be a chase through a public event, a negotiation with someone who needs an exit, a rescue from a guarded property, a raid after legal cover fails, or an attempt to prevent evidence from leaving town.

Cultists use ordinary human statistics. The rulebook's worked combat example pits investigators against a cultist with DEX 60, Fighting (Brawl) 30%, Dodge 30%, a 1D4 damage bonus, Build 1, and 13 hit points, and its opposed-roll example treats an unremarkable cultist's STR and SIZ as falling between 50 and 89. That is a person the investigators can grab, outnumber, or outrun, which is exactly why cultists make good opposition. A key cultist can be tougher, and a cult priest may know spells.

Establish goals, witnesses, exits, and collateral consequences before violence begins. A cultist may want to protect a document, delay investigators, silence a witness, escape with a target, or preserve the group's public reputation. If combat occurs, use the published procedures, but do not let it erase the social stakes.

Common Cultist Mistakes

Making every member identical. A cult becomes flat when all members share the same knowledge, loyalty, and willingness to commit harm. Separate believers, opportunists, coerced people, organizers, and leaders.

Making evil visually obvious. Strange robes have a place, but public respectability, kindness, and competence are better sources of access and tension.

Reducing the investigation to one infiltration roll. Give the players social, financial, institutional, and physical ways to uncover the organization. An infiltrator should gain a perspective, not replace the whole investigation.

Treating recruits as disposable scenery. Members may have caused harm, but they can also be victims, witnesses, family, and people capable of changing their minds. Give investigators choices about rescue, exposure, and accountability.

Ending with the leader's arrest or death by default. The meaningful question is what happens to records, dependents, public trust, and the still-dangerous idea that made the organization possible. Cultists make cosmic horror playable because they turn an incomprehensible threat into choices people have made, so investigators can win something real even when the truth behind the organization stays beyond them.

Monsters and Their Stats

Monster statistics are a private Keeper tool, not the encounter. They resolve uncertain actions and establish scale. The encounter is what investigators notice, what the thing wants, what it changes in the situation, and what choices remain once the group understands it is in danger. If the players can sum up a monster as "the one that did a lot of damage," the encounter was probably too thin.

How to Read a Monster Entry

Each Keeper Rulebook entry lists STR, CON, SIZ, DEX, INT, and POW. Most alien creatures have no APP or EDU, because those qualities mean nothing for them. The values given are for an average specimen, with dice ranges you can roll or use to build a lesser or greater one, and the book gives Keepers full permission to alter or rethink any entry. Only full values are listed. Halves and fifths are rarely needed because monster characteristics mostly set the difficulty of investigators' rolls.

Every entry also gives a Build, the at-a-glance scale value. An average human is Build 0 and the human range runs from -2 to 2. Something two Builds smaller than you can be thrown, one smaller lifted easily, an equal Build carried briefly, one larger barely lifted, and two larger only unbalanced or disarmed. A standard car is Build 5, so any monster of Build 3 or more can damage vehicles.

Then comes a Sanity loss written as two values, such as 0/1D6. The first is lost on a successful Sanity roll and the second on a failure. Under the rulebook's Getting Used to the Awfulness rule, once an investigator has lost as many Sanity points to one kind of monster as its maximum loss, they stop losing Sanity to it for a reasonable interval. The book's example: nobody loses more than 6 points for encountering Deep Ones, even if a hundred appear. The Sanity rules guide covers the rest of that procedure.

Read the entry once for story before numbers. Pull out its environment, objective, sensory signature, relationship to people, and practical limits.

Then read the mechanics and highlight only what might occur in the prepared scene. Treat a notable capability as a promise about the fiction. If a creature can change an environment, show the changed environment. If it controls escape routes, show the routes before initiative.

Mythos Monster Quick Reference

These are the average values from the Keeper Rulebook for the creatures covered on this page. Use the book for characteristics, full attack lists, and spells.

The rulebook is blunt about which of these investigators can fight. Deep Ones, Mi-Go, ghouls, byakhee, nightgaunts, and human cultists, among others, can be "taken on" by several investigators with some hope of success, which is why so many scenarios use them. Against the rest, fleeing or hiding is usually the only way to survive. Even the human-scale ones should not be humanized: their goals and knowledge should stay hard to fathom.

Choose the Encounter Before the Creature

Start with what the scene must accomplish. A creature can make an excellent guardian, pursuer, witness, contaminant, obstacle, or catastrophe, but the same being should not do every job in every scenario.

Write one clear investigator objective. "Defeat the monster" is vague. "Get the missing nurse through the service tunnel before the creature returns" gives the group a plan and tells you why behavior matters.

Signal Danger Before Contact

Fair horror gives investigators a chance to recognize risk before the worst consequence arrives. This does not spoil the reveal. It creates the moment when players decide whether to press forward, prepare, call for help, take another route, or leave.

1. Pattern: Something ordinary repeats incorrectly: animals vanish, a door is always wet, a witness remembers the same sound.
2. Trace: The group finds a physical sign that makes the pattern harder to dismiss.
3. Near miss: Someone almost encounters the creature, or its action affects investigators indirectly.
4. Choice: The group knows enough to decide how and whether to enter danger.
5. Contact: The creature appears, acts, or becomes impossible to ignore.

Vary the signals. If every monster announces itself with blood and claw marks, the table learns one visual language. Use air pressure, insects, missing time, damaged objects, a smell that follows people home, a rhythm in plumbing, or an NPC's oddly precise rule about where nobody should stand. Every signal should create a lead: a smell points to a location, a damaged object to a material, a witness's rule to local history.

Build an Action Palette

Do not run every creature as an attack loop. Before the encounter, write four to six things it might do in the fiction using the published rules you already have.

The rulebook's maneuver rules support most of these. A monster uses its Fighting skill for maneuvers, and a monster of Build 2 or more never takes penalty dice for maneuvering against a human. With a successful maneuver it can knock an investigator prone (gaining a bonus die on its next attack), push someone out of a window, disarm them, grab them with a tentacle, or, if large enough, carry them off. A maneuver fails outright against an opponent 3 or more Builds bigger.

Choose one signature action the players will remember: a sound before movement, a specific way it changes a room, or a refusal to cross a threshold. Repeat it sparingly enough that it keeps its meaning.

Use Scale to Change Objectives

Scale should change the scene objective rather than the amount of harm a creature can inflict. A human-scale adversary can make a room or vehicle dangerous. A much larger being can make a building, street, or whole region unsafe.

An enormous entity does not require a conventional battle. The group may still win by stopping human support, breaking a required sequence, getting civilians away, or preserving a witness and vital evidence. Use environment as part of scale too: a small creature in a flooded basement can control a scene better than a larger being in an open field.

Keep Combat From Becoming Repetitive

When combat is the right outcome, decide what changes each round besides harm. A creature may escape with an artifact, seize a witness, force investigators from cover, block a route, or destroy evidence.

The rulebook gives every monster a generic Fighting skill so you can describe each blow differently without recalculating anything. Its own example is a Deep One that rakes with its claws, body-slams, kicks backward, or smashes a head into hotel plaster, all for the same 1D6 + 1D4 damage. Describe effects through the environment as well: a strike might shatter a railing, flood a corridor, scatter evidence, or jam a door. Establish hazards clearly and apply them to everyone, and do not invent hidden penalties because a fight needs drama.

Consider the monster's objective each round. The book's guidance is that a monster trying to kill should fight back rather than dodge, while one trying to escape may dodge to create an opening to flee. A monster with several attacks per round can also fight back that many times before attackers gain the outnumbered bonus die. The combat rules guide covers the procedure.

End a fight when its objective resolves. The creature might flee with evidence, collapse an exit, take a captive, or withdraw after completing a task. When one does go down, the rulebook suggests describing what investigators see (it stopped moving, it seems to be melting) instead of declaring it dead. Some monsters rise again later, and only a successful First Aid or Medicine roll confirms whether it is alive.

Make Retreat, Hiding, and Rescue Real Options

The rulebook states it directly: not every encounter has to be a fight, and hiding or fleeing may be the wisest option. Fleeing is only a choice when investigators know where they can go and what happens if they leave. Before contact, establish exits, safe zones, vehicles, allies, barriers, or routes that may work. During contact, show when attention is divided or when a risky action could create an opening.

Hiding is also an active scene. Give investigators a route, a temporary refuge, a noisy or exposed action they could take, and a reason the creature may search elsewhere. If hiding only means "roll until the Keeper ends the scene," it produces neither suspense nor agency.

Rescue scenes need a person, a route, and a cost. Investigators may save a captive but leave evidence, preserve a boundary but abandon equipment, or bring an injured ally at the cost of speed. The when to fight or flee guide gives player-facing context for survival and containment as valid outcomes.

Reskin With Purpose

The Keeper Rulebook says Mythos creatures are not uniform in appearance, individuals of the same race can differ, and Keepers may alter entries freely because Lovecraft never codified his monsters. Reskinning is useful when it serves a scenario, not when it exists only to invalidate player knowledge.

Reward informed players for recognizing a pattern, then surprise them with a new context or objective. The goal is a setting that feels alive and particular, not Keeper secrecy for its own sake.

Run the Monster Aftermath

The encounter is not over when the immediate danger ends. Ask what changed, and turn the answer into the next clue, consequence, or relationship shift.

• What physical evidence remains, and who wants it removed?
• Which survivor is frightened, injured, compromised, or newly informed?
• What ordinary institution notices the disruption?
• What did the creature take, protect, or fail to accomplish?
• Which place is no longer safe or ordinary?

Give investigators time to examine, treat injuries, compare accounts, and decide what they believe. A rushed follow-up attack makes every creature the same interruption. The campaign pacing guide gives the broader framework for recovery and consequence.

Deep Ones

Deep Ones are the rulebook's amphibious servants of Cthulhu and of Father Dagon and Mother Hydra, immortal unless slain, living in drowned cities and interbreeding with human worshipers. Their hybrid offspring usually begin to change in their late teens and eventually go to the sea. Dagon and Hydra are Deep Ones grown vast with age, each over 20 feet tall. Because Deep One scenarios are built around coastal communities, family inheritance, and hybrids, they have their own Deep Ones guide, which covers shoreline clues, human intermediaries, and how to treat hybrids as people rather than monsters.

Mi-Go

The Keeper Rulebook describes the Mi-Go, the Fungi from Yuggoth, as an interstellar race closer to fungus than animal, with a base on Yuggoth (Pluto) and mining colonies in Earth's mountains where they seek rare metallic ores. They talk to each other by changing the colors of their brain-like heads but can speak human languages in buzzing voices. They cannot eat Earth food, fly clumsily in Earth's atmosphere, worship Nyarlathotep and Shub-Niggurath, and hire or compel human agents to front their operations. Their surgeons can remove a living human brain and keep it in a metal cylinder fitted with devices for speaking, hearing, and seeing.

The cruelest Mi-Go scenario is about whether investigators can prove that a person who survived the experiment is still being treated as a person, more than whether they can stop it. A witness who returns with impossible knowledge, a patient whose family is told not to ask questions, or a collaborator who accepted an offer they cannot explain makes the operation personal.

Mi-Go Are an Operation, Not a Raid

Give the Mi-Go an operation with an objective, a site, a supply line, a human-facing layer, and a point of failure. The investigators need enough of it to choose what they can save, expose, disrupt, or carry into another case, and can leave the rest unconfronted.

The answer should not be "world domination." An operation becomes more disturbing when its goal is narrow and practical from an alien point of view: a particular seam of ore, a record of how humans respond to a condition, or an object buried beyond human memory. The stakes grow when the human cost is incidental. This also gives the Mi-Go a reason to retreat, conceal, or remove evidence instead of fighting to the last. Intelligent researchers protect the project, not their pride.

Start With an Impossible Project

Open on a problem that has an ordinary explanation until it does not. A prospector disappears after reporting a new vein. A medical researcher receives notes in a colleague's handwriting from a laboratory that burned down. A freight clerk finds a shipment with no sender. A newspaper prints a mountain rescue story before the rescue takes place.

1. Work anomaly: A mine, hospital, university, rail line, weather station, or business produces a result someone can document.
2. Human discrepancy: A worker's statement, payroll record, phone call, or family account does not fit the official version.
3. Material contradiction: Samples, photographs, equipment damage, residue, or a site map point toward an unfamiliar process.
4. Operational reveal: The group learns what is being moved, studied, mined, or concealed, and who is in immediate danger.

Every clue must enable an action. A payroll record identifies a missing worker's address. A survey map shows an access route. A phone call reveals a time-sensitive departure. Do not make a single laboratory analysis the only route forward.

Use Evidence That Does Not Behave

Mi-Go otherness should complicate documentation without making investigation impossible. The rulebook gives you a built-in example: ordinary photographic plates will not take an image of a Mi-Go, and a dead one dissolves within hours, leaving only an oily stain.

Give players ways to corroborate. A flawed photograph can be compared with a witness timeline. A sample can be traced to a delivery log. A strange message can be recognized by someone who heard it before. Avoid alien science that only one specialist can solve: let a physician notice a human consequence, an electrician spot impossible power use, a journalist follow a paper trail, and a criminal contact recognize a false shipment.

Put Human Agents at the Center

The human layer gives the scenario a social face. Agents arrange permits, obtain supplies, read local conditions, conduct research, and keep attention away from remote places. They are not equally informed or equally willing.

Give each person a pressure point and a change trigger. The owner might cooperate until a child is endangered. The researcher might refuse to speak until shown that the Mi-Go will take the work without them. Do not make negotiation with a Mi-Go a normal business meeting: human agents translate demands imperfectly and overstate their own importance, and the actual decision makers keep motives the investigators cannot share.

Make Alien Science Create Choices

The most effective Mi-Go technology in a scenario is a situation that forces a human decision, not a list of gadgets. A missing investigator may still be able to communicate from a cylinder but cannot come home the way their family expects. A damaged device may hold evidence that exposes the operation, but moving it could alert those maintaining the site.

• Rescue the person now, or preserve the evidence that could protect others later.
• Destroy an alien installation, or leave it intact long enough to learn where a shipment is going.
• Trust a compromised researcher with the only workable route, or risk a more dangerous approach.
• Tell a family the truth, or keep them safe from the attention the truth will bring.
• Let a desperate agent leave, or stop them from carrying a dangerous secret elsewhere.

You do not need to explain how the science works. State what investigators can observe, what action might change the situation, and what cost they can foresee. Clinical sounds, cold light, unfamiliar smells, and a room built to process human lives do the rest.

Build a Remote Mining Site

Mountain mines and isolated outposts are natural Mi-Go locations, but isolation only matters when it affects choices. Map the site as a network of routes, roles, and resources.

Keep one route relatively reliable, and change conditions gradually: weather closes a road, an agent redirects a vehicle, a radio goes silent, a supervisor starts removing records. For action scenes, establish terrain and exits first. A snowfield, cliff path, mine lift, or cable station matters more than an empty chamber, especially since a Mi-Go's seize maneuver can carry off a victim of its Build or smaller and drop them from a height.

Escalate Through Exposure and Extraction

Mi-Go escalation is about the operation becoming harder to hide and easier to remove. The danger is that the people, evidence, and opportunities investigators need are being sorted, transported, silenced, or replaced.

A train timetable, supply run, incoming storm, shift change, or legal inspection tells the group why delay matters. Do not conceal the final departure until it is too late.

Mi-Go Scenario Patterns

For a one-shot, use a simple extraction clock: a truck leaves at dawn or a train crosses a pass before weather closes it. For a campaign, let the site close down while recovered papers, a missing person, or a human agent point to a second operation. The Mi-Go should feel organized enough to have continuity, but never so transparent that investigators can map the whole network.

Mi-Go in Direct Contact

Direct contact should make clear that investigators have crossed from a human problem into an alien operation. Use unfamiliar movement, altered light, buzzing, cold industrial surfaces, and the reaction of a human agent who knows more than they admitted. Mi-Go can buzz listeners within 40 feet into a trance (an opposed POW roll resists it), speak telepathically, and create a patch of total darkness that no light escapes, so contact can end with investigators unable to act or see rather than wounded.

If combat occurs, let the Mi-Go pursue the operation's goal: withdraw with an item, protect an extraction route, remove evidence, or leave human agents behind. Avoid these common mistakes: turning them into space gangsters, letting strange evidence end the investigation, springing bodily horror as a surprise punishment, making every human agent knowingly evil, and explaining all the science. The investigators should understand the stakes without fully understanding the method.

Shoggoths

The Keeper Rulebook describes Shoggoths as amphibious masses of protoplasm roughly 15 feet across that can form limbs, eyes, and other organs at will, imitate other life forms, and perform great feats of strength. They were made as servants by the elder things, whose civilization their rebellion nearly destroyed, and they now serve Deep Ones and other races while growing ever more intelligent, rebellious, and imitative. The rarer Shoggoth lord is smaller and smart enough to pass as a human, appearing as an obese, hairless person who melts back into its true form if caught off guard.

A Shoggoth encounter should feel like a containment failure, not a fair fight. With firearms doing 1 point per hit and 2 hit points regenerating each round, the rules agree.

Shoggoths Are Containment Problems

Use a Shoggoth when a place has stopped working the way a place should. A research facility, tunnel, basement, ship hold, sewer, mine, warehouse, submerged ruin, or industrial site has rules: doors divide rooms, pipes carry water, staff know routes, alarms mean danger. A Shoggoth violates those rules by moving through, around, or inside them.

At first the investigators only need to know that a controlled environment has become unreliable and that people inside it need help; the word Shoggoth can wait.

Start With a Failing Boundary

Show the boundary failing in ordinary ways first. A locked corridor is wet inside. A maintenance log has entries no worker remembers writing. Waste disappears from a sealed container. A tunnel is unusually clean, as if something swept it without tools, which echoes the rulebook's own description of a Shoggoth's glistening, litter-free path.

1. Operational anomaly: A system produces a result staff can report but not explain.
2. Material trace: Residue, damage, missing equipment, distorted footprints, or altered surfaces point to a physical route.
3. Witness contradiction: Two people describe the same event differently because one met an imitation or partial contact.
4. Site revelation: The investigators learn which boundary was supposed to matter and why it no longer does.

Every clue should lead somewhere practical. A log gives a time. A residue identifies a pipe route. An imitation points to a missing person. A maintenance map reveals a second exit.

Use Imitation as Evidence, Not a Gotcha

The most frightening thing a Shoggoth can imitate is a safety measure, even more than a person. A sealed door that opens when it should not, an emergency voice giving the wrong evacuation order, or a rescue team that does not behave like one makes investigators doubt a plan they were ready to trust.

Do not use imitation to punish players for trusting anything. Establish tells that alert investigators to the possibility: wrong terminology, missing context, strange timing, an odd reaction to pain, a smell, or knowledge of the wrong detail. Make verification an active part of the investigation: let players ask sensible questions, compare stories, check a route, or seek a second witness.

Imitation also works at partial scale. A false handprint, a copied voice on a telephone, or an object that seems recreated from memory points toward a threat still learning how humans work. A Shoggoth lord takes this all the way, and the rulebook suggests an optional 1/1D3 Sanity loss for watching one change from human to Shoggoth form.

Build a Site That Changes Under Pressure

Map the site as routes and functions rather than a combat grid.

Change one or two areas whenever investigators delay or make noise, not every room at once, and keep at least one route clear enough to plan around.

Give Investigators Escape and Rescue Objectives

Direct destruction is rarely the interesting objective, and against a Build 9 creature that can engulf several people and crush them each round, it is rarely survivable. Better goals are to rescue workers, retrieve evidence, restore a barrier, reach a vehicle, warn a nearby population, or keep the failure from entering a larger system.

Establish exits and costs early. A service ladder may be slow but safe. A vehicle may carry everyone but need fuel. A control room may stop the spread but leave a witness behind. A floodgate may protect the town but trap someone on the other side.

Someone should have a reason the Shoggoth was hidden, tolerated, studied, transported, or exploited: a scientist, collector, cultist, business owner, caretaker, thief, or terrified survivor. Do not make them omniscient. A handler may have believed it was controllable. The useful question is who knew enough to act, what they chose to protect, and what will change their mind now.

Escalate Through Spread and Adaptation

Make adaptation visible. If the creature learns a route, show signs before it blocks that route. If it imitates a voice, give the group a clue that the original person is elsewhere.

Shoggoth Scenario Patterns

The closed facility suits a one-session game: a compact map, a finite list of missing people, and a visible control point. Start outside with someone insisting the report has an ordinary explanation, then make the first mystery procedural: why are the lights on, why is the clock wrong, why does the guard's log show an exit no camera recorded? The inherited property gives more room for social play. A descendant may not know why a relative paid for a sealed cistern or kept documents restricting access to part of the land, until a developer, creditor, or official is about to remove the boundary for a completely human reason. For a campaign, the transport pattern makes the Shoggoth a consequence of a larger human operation: the first case ends in apparent containment, but a compromised manifest or missing crate proves something left by another route.

Shoggoths in Direct Contact

Direct contact should confirm the scale of the failure. Describe motion, changing surfaces, faint self-luminous light, sound, and the way a familiar space stops behaving normally. If combat occurs, let the creature pursue an objective: block escape, engulf evidence, capture a person, or withdraw through a system route.

The fastest way to flatten a Shoggoth is to treat it as a large opponent waiting in an empty room. Avoid the related mistakes too. Do not make every clue a falsehood; give players a real survivor, a route that works once, or a record they can corroborate. Do not hide the immediate objective behind the revelation. Do not change the map without telegraphing it through wet marks, failed lights, or a broken radio message. Do not make containment a single correct button: lights versus pumps and a secure door versus a trapped ally are better. And do not end at the first escape. Ask what crossed the boundary with the survivors.

Great Old Ones

A Great Old One should not arrive as a larger opponent at the end of an ordinary combat encounter. Its presence changes the terms of the scenario. Streets become unsafe, dreams become evidence, a community adopts impossible rules, and people make terrible choices to preserve what little normal life remains. The best Great Old One finale may not show the entity clearly at all: a brief, partial, or indirect manifestation leaves more room for dread than a full visual inventory.

What the Rulebook Says About Great Old Ones

The Keeper Rulebook describes Great Old Ones as immensely powerful alien beings with supernatural-seeming abilities that are less supernatural than the Outer Gods, and far more likely to be worshiped by humans because they are comparatively near and sometimes involve themselves in human affairs. Each is independent, and many are imprisoned in some way until "the stars are right." Investigators most often meet their worshipers and alien servants rather than the beings themselves, and the book says gods and Great Old Ones should be met infrequently.

Two rules shape every deity encounter. First, if a Great Old One or Outer God is reduced to 0 hit points, it is not killed or knocked out, but dispelled or forced back, and it can return. Damage alone will not destroy these powers. Second, deities have no Dodge skill, investigators never gain the outnumbered bonus against them, and no roll is allowed when a god's opposing characteristic exceeds the investigator's by 100 or more. The book compares a god's regard for investigators to a person's regard for an ant.

A Great Old One Is a Condition

Treat the power as a condition affecting a place, population, or sequence of events. The condition has to be an observable change that creates a scenario, rather than the bare fact that a god is awake.

Choose one primary condition and one supporting sign. If geography is wrong, let a recurring dream or local rule reinforce it. Cthulhu's dream-sending is a ready-made example: the rulebook says affected artists wake driven to paint or sculpt nightmares, and others slide toward madness. Do not add unrelated curses, random attacks, and a second apocalypse because the finale feels important.

Start With a Local Human Problem

Begin with someone who needs help before anyone uses cosmic language. A harbor authority needs an explanation for impossible tides. A doctor wants help with patients who share the same dream. A tenant group wants to stop disappearances in a renovated building. A family asks investigators to find a relative who came back from research speaking in rules nobody understands.

The human problem gives the scenario an entry point and a moral center. It establishes what the community risks losing: housing, trust, livelihood, health, memory, a child, a landmark, or the ability to tell the truth publicly. Do not make every resident secretly involved. A community under a Great Old One's influence should contain ordinary people trying to preserve ordinary life, not only disposable cultists.

Choose an Influence Theme

An influence theme makes a cosmic power coherent without a lore lecture. It tells you which clues recur, which human bargains look tempting, and what the finale asks investigators to value.

Use the theme to guide sensory presentation. Repeated sound, color, weather, texture, or dream imagery makes the influence feel deliberate and does more than explaining a cosmic family tree to investigators who need to decide where to go next.

Set a Human-Scale Objective

Investigators need an objective whose outcome matters even if the power stays beyond them, which is a very different target from defeating a Great Old One.

• Stop a human group from completing a required action.
• Get people out before the condition worsens.
• Secure or destroy a tool that enables contact.
• Prevent an institution from burying evidence needed for containment.
• Learn a decisive rule before a deadline.
• Preserve a boundary, even though it abandons something valuable.
• Survive a manifestation long enough to protect a witness or carry evidence away.

Avoid objectives that require guessing the Keeper's private solution. If a ritual must be interrupted, show the people, materials, location, schedule, or consequences that make it legible. If escape is correct, establish routes before the scene becomes impossible. The rulebook's own model is the sailor in The Call of Cthulhu who rammed Cthulhu with a steamboat and escaped: the win was getting away, not a kill.

Build a Visible Escalation Track

Great Old One scenarios need pressure, but invisible doom clocks produce random rushing rather than horror. Show each stage through a public event, changed NPC behavior, altered environment, or discoverable evidence.

Use Collaborators as the Action Layer

The cosmic power is usually too vast for negotiation or combat. Human collaborators supply the action: people who deliver objects, cover up incidents, recruit victims, manage a site, exploit the influence, or believe they are preventing something worse. The rulebook notes that even the Cthulhu cult is fragmented, with sects that disagree on methods and dogma, which gives you rival collaborators for free.

Give each collaborator a human reason: status, safety, knowledge, money, grief relief, community, revenge, or control over a condition already harming them. Layer knowledge across the organization. A guard knows building rules, a caretaker knows the schedule, a scholar recognizes the pattern, and a leader believes they can control it. The Cultists section covers building that organization.

Keep the Influence Coherent Across Sessions

Longer arcs lose focus when the influence can explain anything at any time. Set a few consistent rules for what the condition changes, who notices first, and how people rationalize it.

Return to signs without making them a code puzzle. The third appearance of a sound or object should mean something new because the group has learned something since the first. A repeated detail that identifies a safe route, compromised person, or impending breach becomes useful dread.

Let people disagree about the influence. A scientist may see contamination, a local elder an inherited obligation, a cult leader a thing they control, and a frightened resident only the rules that keep their family safe. Their partial truths give investigators several ways in. When the investigators disrupt part of the influence, change the pattern rather than erasing it. Closing one route may force collaborators onto another.

Common Great Old One Mistakes

The unplayable revelation. The Keeper describes an enormous truth and waits. Give players an immediate concern instead: someone trapped, a route closing, evidence at risk, or a person making a catastrophic choice.

The lore lecture. Do not pause for an encyclopedia entry. The players need the next usable conclusion, not every name attached to the Mythos. The rulebook itself warns that defining these beings too closely may prove counterproductive.

The automatic sacrifice. If every finale demands that an NPC die or an investigator be ruined, players learn that attachment is a liability. Vary the costs: public exposure, lost evidence, a compromised institution, a broken alliance, a dangerous secret, or an unresolved threat.

The invisible deadline. Show a schedule, a changing condition, a public event, an NPC action, or a measurable pattern, then let the group decide how much risk to accept. Great Old Ones are frightening because investigators cannot put the world back exactly as it was, so give them a smaller, urgent piece of it to protect.

Outer Gods

Outer Gods work best when investigators never mistake them for a local problem with a local body. Their influence may enter through dreams, mathematics, rituals, devices, cults, impossible transmissions, or changes in the sky, but the power itself stays too distant, strange, or fundamental for a conventional confrontation. An Outer God should make investigators feel small because the world is too large to control, not because the Keeper has removed every meaningful choice.

What the Rulebook Says About Outer Gods

The Keeper Rulebook describes the Outer Gods as closer to true gods than the Great Old Ones: extremely powerful, mostly blind and idiotic in human terms, possibly from beyond the cosmos, and largely uninterested in humanity. When they do notice humans, they tend to try to break through cosmic walls. Lone madmen and sorcerers worship them more than whole communities do, and their associated species (servitors of the Outer Gods, dark young, hunting horrors, shantaks) are correspondingly rare on Earth. The book also says Lovecraft used these labels inconsistently and invites Keepers to decide what fits their story.

Nyarlathotep is the one Outer God investigators are likely to talk to. In human form he can be killed by normal means, but the corpse splits to release a monstrous form that flies away. He tends to deal with challengers by summoning something to carry them off.

Outer Gods Are Pressure From Beyond the Scenario

For play, frame an Outer God as a source of pressure rather than the scene's physical antagonist. A Great Old One may produce a local condition in a town. An Outer God often feels more distant: a principle invading through a signal, a pattern people can glimpse but not master, or an influence that rearranges what reality permits. The difference is practical, not a demand for a perfect taxonomy.

The answer might be a broadcast, a research result, a dream, a cult ceremony, a physical object, a mathematical sequence, or a person who has become a channel. One clear interface is enough to connect a scenario to something vast.

Choose a Human Interface

Investigators need a way to touch the scenario even when the power is beyond reach. The interface is the human-scale point where contact becomes evidence and action.

Choose an interface with friction. A broadcast can be copied but may expose listeners. A research project has records but may be locked behind professional loyalty. An artifact can be moved but attracts people who think it belongs to them. Friction creates scenes instead of delivering every answer through one convenient document.

Build an Impossible Pattern

Outer God influence should create a pattern that ordinary expertise can recognize as wrong before anyone knows why.

1. A reliable system produces an unreliable result. A clock, map, patient record, weather log, or recording contradicts itself.
2. Several people respond in a related way. They repeat a phrase, travel to the same place, avoid a harmless object, or dream the same detail.
3. A human action links the observations. Someone distributes the signal, funds the project, moves the object, or protects the institution.

For example, an observatory's readings may be internally impossible, several residents begin drawing the same stairwell, and a private foundation urgently funds the research team to continue. The investigators have a pattern, people to question, records to examine, and an action to interrupt, without needing an entity name. Repeat one sensory or conceptual sign as the pattern deepens (a rhythm, a color, an angle in architecture, a phrase) and make sure it eventually helps the group decide something.

Make Intermediaries the Immediate Threat

The immediate opposition should usually be human or human-scale: scholars, patrons, cult leaders, administrators, desperate families, compromised officials, or people who believe contact will grant them something valuable. They can negotiate, lie, flee, use systems, and make decisions investigators can influence.

A scenario gains depth when investigators can persuade one person, expose another, and discover too late that a third has made a different bargain. The rulebook's Azathoth entry adds a useful flavor note: the few who knowingly worship it may hold real insight into the universe, understandable perhaps only to other madmen.

Give the Group a Limited Objective

The investigators cannot solve an Outer God by fighting it. They can still achieve a limited goal that changes the human situation.

• Stop a signal from being broadcast at a particular time.
• Get a device out of an institution before it is activated.
• Prevent a cult from acquiring its final participant or material.
• Protect a witness whose knowledge is needed to identify the next breach.
• Break a false public narrative before it draws more people into danger.
• Evacuate a location before an impossible condition becomes permanent.
• Decide whether to destroy evidence or preserve it for a future containment effort.

Make the objective observable. "Stop the cosmic plan" is not an objective. "Prevent the foundation from opening the observatory dome during the scheduled transmission" is one. Prepare more than one route: a sympathetic employee, a break-in, public exposure, an intercepted delivery, or a collaborator convinced they are being sacrificed.

Escalate Through Systems, Not Bigger Fights

Outer God scenarios become more frightening when normal systems start carrying the influence: institutions, communication, schedules, infrastructure, social networks, or shared beliefs.

Do not turn every stage into combat. A contract gets signed, a broadcast goes live, a department changes policy, a family receives instructions. These create pressure while leaving room for investigation and social play.

Keep Cosmic Scale Personal

The group cares about a vast threat through people and places. Connect the influence to a patient who needs protection, a colleague whose reputation is at risk, a neighborhood that will be displaced, a family that has carried a burden for generations, or an institution that can still make a better choice.

Use personal stakes with consent. A relationship should complicate a choice, not become an automatic hostage. A parent may ask an investigator to stop digging, a former mentor may be compromised, or a professional obligation may conflict with secrecy. Give quiet scenes room: a person who heard the impossible broadcast needs time to explain what they fear. Cosmic horror becomes frustrating when "nothing matters" is the answer, and memorable when something matters desperately even though the universe is indifferent.

Keeper Advice for Mythos Scenarios

Make Combat One Outcome

Mythos entities are not necessarily mindless or automatically violent. Many have goals beyond killing investigators. An encounter can involve hiding, fleeing, bargaining, observation, captivity, rescue, or escape. Start by asking what the entity is trying to accomplish in the scene.

Combat has a place when it changes the situation. A human-scale opponent may guard a route, delay a rescue, or force a retreat. With a larger creature, fighting may only be a distraction while the real objective is to close a door, evacuate civilians, reach a vehicle, or stop an artifact from moving. Give investigators a route to survival before revealing an overwhelming threat, since survival can be success.

Make Mythos Knowledge Useful and Costly

Mythos knowledge should change what investigators can attempt. A text, dream, artifact, or witness is useful when it reveals a location, sequence, constraint, relationship, or cost, not because it contains impressive names.

Never make the dangerous text or artifact the only route to progress. Give an alternative that is slower, risky in another way, or dependent on a relationship, so the group decides whether forbidden knowledge is worth its price. The rulebook ties that price to real mechanics: the first Mythos-related insanity adds 5 points to Cthulhu Mythos skill, and maximum Sanity is always 99 minus that skill. See the Mythos tomes guide for handling books as plot tools rather than loot.

Run Manifestations as Crises

A manifestation is a crisis that changes space, perception, and priorities, rather than a standard encounter with a larger map. Give every one four anchors:

1. A concrete danger: a collapsing pier, flooding ward, trapped crowd, spreading fire, closing route, or a location that no longer leads to the same sky.
2. A human objective: rescue, warning, evidence, barrier, vehicle, or vulnerable person.
3. A choice of costs: time versus safety, evidence versus people, secrecy versus help, or one route versus another.
4. A clear exit condition: the ritual breaks, the group reaches safety, the required action is prevented, or the scene becomes aftermath.

Use partial description. A wrong reflection, impossible scale, a sound arriving before its source, stars reflected where no glass exists, or a room that feels larger from one direction says more than anatomy. Do not require players to understand the whole event before they act. In an observatory that no longer opens onto the right sky, investigators can still get a witness through a service corridor, cut power to a transmitter, or stop a collaborator from completing the last step. Apply the published Sanity losses when a god is actually seen, and remember the table above: most cost 1D10/1D100, which is exactly why a partial glimpse is often the kinder and scarier choice.

Plan Endings and Aftermath

An arc can end in containment, escape, partial failure, sacrifice, exposure, or temporary reprieve. The ending should answer the question the group pursued, even if the cosmic power remains beyond them.

Name what changed. Who was saved? What truth cannot be shared safely? Which institution now knows enough to become ally or enemy? What evidence survives? Which investigator has a new responsibility because of what they saw or chose? Do not launch the next emergency immediately. Let the group investigate the aftermath, recover, and decide what success or failure means. The campaign pacing guide explains why quieter sessions give horror weight.

Build a Mythos Scenario Loop

1. Start with harm: Someone needs help, a place has changed, or a pattern cannot be ignored.
2. Show ordinary evidence: Give people, records, locations, and traces that make sense before the Mythos explanation does.
3. Introduce contradiction: Let a clue disprove the comfortable theory.
4. Reveal an operational need: Show what the force, cult, or compromised community must do next.
5. Apply visible pressure: Escalate through a deadline, spread, exposure, or changing environment.
6. Demand a human-scale decision: Ask what investigators protect, reveal, destroy, preserve, or flee.
7. Play aftermath: Show which relationships, places, and assumptions changed.

The loop works for a single mystery or a campaign arc. Every manifestation should leave the world in a state that produces the next choice.

Mythos Encounter Worksheet

Fill in the core block for every scenario, then add the block for the threat you are using.

CORE
Scenario effect in plain language:
Local human problem and stake:
Ordinary place or institution affected:
Encounter role now:
Alien goal:
Constraint, requirement, or priority:
What it does if investigators ignore it:
Ordinary disruption / sensory contradiction / human cost / direct contact:
Physical, social, documentary, environmental, and operational clues:
Visible escalation event and clock:
Human-scale investigator objective:
Likely aftermath and next lead:
Only needed published mechanics (Build, HP, armor, Sanity loss):

CULT
Public face and private objective:
What the group offers members / who knows the full purpose:
Leader and failed promise:
Organizer and pressure point:
Recruiter and what they do not know:
Person most in need of a safe exit:
Infiltration opportunity and cost:

CREATURE
Published creature reference:
Environment, routes, and exits:
Signature sensory sign:
Action palette (advance, separate, deny, mark or bargain, withdraw):
What changes if investigators fight / hide or flee:
What they can rescue, preserve, or learn:

MI-GO OR SHOGGOTH SITE
Operation objective or original boundary:
Why this location matters / why the boundary is failing:
Human agent, owner, or handler, and their change trigger:
What is about to leave the site or spread:
Control point and reliable route:

GREAT OLD ONE OR OUTER GOD
Influence theme or human interface:
Primary condition and supporting sign:
Impossible pattern:
Collaborator or intermediary and motive:
Useful knowledge, its cost, and an alternative route:
Crisis anchors (danger, objective, costs, exit condition):

Leave unknowns in the worksheet. You need enough to run behavior consistently, give credible leads, and make choices matter, not every fact about an entity.

Cthulhu Mythos Checklist

Before play, make sure the scenario has:

• A human problem that exists before investigators name the supernatural cause.
• An encounter role instead of a creature chosen only for its appearance.
• A goal and constraint that create observable behavior.
• Several sensory signs, not only a visual description.
• Physical, social, documentary, financial, or environmental clues that survive a missed route.
• Human NPCs with different knowledge, loyalties, and reasons to change sides.
• A visible escalation path with decisions at each stage.
• A reason to hide, flee, bargain, contain, rescue, or investigate besides fighting.
• Exits, routes, and rescue options established before they are needed.
• A human-scale objective if a Great Old One or Outer God enters the scenario.
• The Build, armor, and Sanity loss of anything investigators might actually meet, checked in the rulebook.
• An aftermath that changes people, places, or assumptions.

The Cthulhu Mythos works when investigators cannot fully master it but can still choose how they meet it. Give them evidence, danger, and an imperfect way forward.

Where To Go Next

A Mythos encounter is only half the design work. The Keeper Resources Guide covers pacing, NPC creation, and scenario structure for building the case around whatever comes out of the worksheet above, and the Magic and Mythos Tomes Guide covers spells and books as plot tools rather than loot. The Call of Cthulhu 7e Guide Hub lists the rest of the collection by topic.