[[quoteright:350:http://static.tvtropes.org/pmwiki/pub/images/Call_of_Cthulhu_2.jpg]]
[[caption-width-right:350:"[[Blog/ThingsMrWelchIsNoLongerAllowedToDoInAnRPG 840: Even if it would have immediately solved the last six adventures, I will not throw dynamite into every well we come across]]."]]

->''The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents. We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far...''
-->-- '''Creator/HPLovecraft''', ''Literature/TheCallOfCthulhu''

->''Okay, now roll [[SanityMeter SAN]].''

One of the most famous TabletopGames of all time, ''Call of Cthulhu'' combines the adventurism and teamwork of Tabletopgame/DungeonsAndDragons with the LovecraftianFiction setting of the CthulhuMythos. Your adventurers, or rather investigators, are dropped into scenarios right out of a Lovecraft story, and must keep their wits about them; the goal of every ''C.O.C.'' campaign is not so much to ''defeat'' the Enemy, but to ''survive'' Its horrendous onslaught while following the mystery out to its bitter -- [[KillerGameMaster and usually grim]] -- end.

Notable for introducing [[SanityMeter Sanity as a character stat]] -- your characters actually risk having their minds blown apart, partially or completely (and sometimes even ''literally''), by the events they encounter. As a result, the term "SAN check" has drifted out of the ''Cthulhu'' following and become a generally recognized metaphor among gaming circles. As characters learn more lore about the Cthulhu Mythos, their maximum Sanity shrinks -- [[SadisticChoice forcing players to choose]] between their characters being ignorant or crazy.

Also has variations for settings and time periods including the [[TheRoaringTwenties 1920s]], [[PresentDay Modern]], DeltaGreen, [[TheGayNineties Gaslight]], [[DarkAgeEurope Dark Ages]], [[AncientRome Roman times]] and [[InSpace space]].

Do not confuse with the video game ''VideoGame/CallOfCthulhuDarkCornersOfTheEarth'', which is also based on the CthulhuMythos (specifically, on the "Raid On [[TownWithADarkSecret Innsmouth]]" campaign module of the RPG), ''Videogame/CallOfCthulhuTheWastedLand'' (an [[IndieGame indie]] TurnBasedTactics videogame which setting is a mix between Cthulhu Mythos and UsefulNotes/WorldWarI), a CollectibleCardGame of the same name loosely based on (and licensed by) Chaosium's aforementioned RPG, a movie done in the black-and-white style of the 1920s about Cthulhu, the Youtube series WebVideo/CallsForCthulhu, or [[Literature/TheCallOfCthulhu the original short story]] by Creator/HPLovecraft that they are all named after.

See also ''TabletopGame/ArkhamHorror'', Cthulhu Mythos TheBoardGame.

----
!!Has examples of:

* AbuseMistake: ''Dreamlands'' adventure "Pickman's Student". When the investigators go to the apartment of Mr. and Mrs. Briggs, they find a man tied to a chair with a bathrobe thrown over him. If they rescue him they discover that he's playing bondage games with his wife.
* AdjectiveAnimalAlehouse: Multiple examples
* AfterlifeExpress: ''Fearful Passages'' adventure "Iron Ghost". "The Train That Ever Was" carries its victims to a terrible fate: to be devoured by Azathoth.
* AllWebbedUp: What happens to you if you mess with Atlach-Nacha or Leng Spiders.
* ApocalypseCult: CthulhuMythos cults try to do this in the campaigns ''Shadows of Yog-Sothoth'', ''Masks of Nyarlathotep'' and ''The Fungi from Yuggoth''.
* ApocalypticLog: ''Shadows of Yog-Sothoth'' adventure "The Warren", ''Horror on the Orient Express'' campaign, ''Cthulhu Companion'' adventure "The Mystery of Loch Feinn", and the ''Fearful Passages'' supplement adventure "Armored Angels".
* ApothecaryAlligator: In the campaign ''The Fungi from Yuggoth'', adventure "The Thing in the Well", Dr. Cornwallis has a stuffed alligator hanging by wires from the ceiling of his alchemical laboratory.
* ArrestedForHeroism: Noted as a potential problem for Investigators in the ''Cthulhu Companion'' and the "Field Manual of the Theron Marks Society" (''Terror from the Stars'').
* AttackOfTheMonsterAppendage: ''Dreamlands'' adventure "Yellow Sails". When Mironim-Mer activates the Oracle Mirror, the wendigo demon possessing it sends out a tentacle to grab him.
* BadHabits: ''The Asylum and Other Tales'' adventure "The Mauretania". A Bolshevik agent pretends to be a priest to get close to a Russian count for an assassination attempt.
* BedlamHouse: Creepy insane asylums are a recurring setting. It's even possible to visit (or more likely be locked up in) the ''original'' Arkham Asylum.
* BedouinRescueService: ''Curse of the Chthonians'', adventure "The City Without A Name". After the investigators leave Irem, if they run out of camels and water in the desert they can be rescued by a small band of Bedouins.
* BeethovenWasAnAlienSpy: OdaNobunaga, it turns out, was an avatar of Nyarlathotep.
* BeingHumanSucks: ''Cthulhu Companion'', adventure "Paper Chase". A book lover named Douglas Kimball hates dealing with people. He meets some ghouls, goes to live with them and eventually becomes one himself.
* BigCreepyCrawlies: Leng Spiders, Insects from Shaggai, and others. This is no game for the entomophobic.
* BizarreAlienBiology: Intelligent flying fungoids, semi-vegetable tentacled elder things, and more.
* BlessedWithSuck. One old issue of Wizard Magazine stated that ''Call of Cthulhu'' is the only game in which the player with the fastest speed lives the longest, and the only game in which ''no one'' wants the magic item. It doesn't help the original game was a ticking countdown from sanity to insanity: your character ''will'' go insane. It's just a matter of how fast. Of course, your character might not go insane. They have a good chance of dying before they hit that point. Needless to say, ending a Call of Cthulhu game with a living and sane character is unlikely at best.
* BlueAndOrangeMorality: Even the most superficially benevolent races in the game have utterly inscrutable or bizarre motives.
* BodyHorror: Mostly for non-player characters, but [=PC=]s aren't safe either.
* BrainInAJar: A possible fate for characters who get on the wrong side of the Mi-Go.
** This does not mean you've pissed them off. Then they just kill you. They stuff your brain in a jar if they ''like'' you.
** Unfortunately, the Mi-Go are just not all that good at emulating human senses (which, given they are sentient fungus-things, makes sense). One supplement posits that the use of speech software, high quality cameras, microphones, and a lot of lucky rolls would allow a brain in a jar to have a lot closer to human abilities.
* BrokeYourArmPunchingOutCthulhu: If you destroy Cthulhu with a nuke, he'll regenerate around 15 minutes later - [[FromBadToWorse but now he's radioactive]].
* BrotherhoodOfEvil: The Brotherhood of the Beast in ''The Fungi from Yuggoth'' (and its remake ''Day of the Beast'').
* ButtMonkey: Harvey Walters, the sample character used for gameplay examples (i.e. being maimed/driven mad).
* CannibalLarder: In the supplement ''Shadows of Yog-Sothoth'', adventure "The Worm That Walks". When the {{PC}}s explore the Woodie house they discover a kitchen which is the butcher shop of a den of cannibals. It has the gruesome remnants of an earlier meal spread around - hands, feet, and even more grisly bits of human debris.
* CelestialBody: ''The Fungi from Yuggoth'', "Day of the Beast". When the Sphinx turns into the Beast (an avatar of Nyarlathotep) its face falls off, revealing a black oval void filled with whirling suns and galaxies.
* CanonDiscontinuity: {{Invoked|Trope}} by the rulebook writers, who felt that some of Creator/AugustDerleth's additions to the canon seemed out of place, or took the edge off some of the horror. Given that this is an officially licensed product made by people who [[RunningTheAsylum were originally mythos fans]], it is debatable how much of this discontinuity is {{Ascended|Fanon}} [[FanonDiscontinuity fanon]].
* CanonImmigrant: There are also several entities that originate from this game, such as ''Arwassa'', ''Baoht Z'uqqa-Mogg'', ''Ghadamon'' and handful of lesser Outer Gods.
* CanonWelding: The ''Malleus Monstrorum'' sourcebook. Not only mentioning every major Mythos entity, the book also throws in ''Film/TheThing1982'', The Martians of ''Literature/TheWarOfTheWorlds'', and ''TheWickerMan'' and several of Creator/StephenKing's characters are Nyralathoep's avatars.
* CargoCult: ''Glozel Est Authentique!''. When Phoenician traders stopped coming, the people in the area that would become Glozel created tablets with Phoenician characters on them to try to bring them back.
* CatGirl: Bast, the Egyptian goddess of cats. She shows up to exact vengeance if someone hurts a cat.
* CatsAreMagic: A staple of Lovecraftian fiction in his "Dreamlands" works, naturally replicated here and with the inclusion of the goddess Bast as an Elder God.
* CaveMouth: ''Fragments of Fear'' adventure "Valley of the Four Shrines". The entrance to the cave that leads to the Valley has been carved in the likeness of Cthulhu's head.
* CigarFuseLighting: ''Terror from the Stars'', "Field Manual of the Theron Marks Society". Theron Marks always had a lit cigar in his mouth during adventures in order to light sticks of dynamite.
* ConcealingCanvas: In ''Utatti Asfet'' and ''The Asylum and Other Tales'' adventure "The Asylum".
* CoolUncle: In ''The Fungi from Yuggoth'' adventure "Mountains of the Moon", an NPC named Victor recognizes one PlayerCharacter. He was an old friend of the PC's father, and the PC remembers him as "Uncle Victor", a warm, good-hearted man (even though Mom didn't seem to like him).
* CosmicHorrorStory: The game at its core.
* {{Cult}}s: Usually worship one or more EldritchAbomination; [[ReligionOfEvil NOT nice people]].
* CuriosityKilledTheCast: Because the game requires investigation, this is the inevitable fate of any group of Investigators, unless they go permanently insane first.
* {{Cyclops}}: ''Pursuit to Kadath'' adventure "The All Seeing Eye of the Alskali". The title Alskali monsters, whose single eye can hypnotize their victims.
* TheDayOfReckoning: Can occur in multiple published campaigns, including ''Shadows of Yog-Sothoth'', ''Masks of Nyarlathotep'' and ''The Fungi From Yuggoth''.
* DespairEventHorizon: What often happens when characters are exposed to too much of the Mythos.
* DeadlyHug: ''Masks of Nyarlathotep''. M'Weru likes to embrace her victim, cast the Hands of Colubra spell (which changes her hands into the heads of poisonous snakes) and use them to bite her victim and poison them.
* DeadManWriting: ''Dark Designs'' adventure "Eyes for the Blind". Elias Cartwright's note starts "By the time you read this I fear that I shall be dead".
* DealWithTheDevil: The spell Unspeakable Oath. By devoting yourself to the power Hastur, he grants you a wish or boon. However, you begin to lose charisma at a gradual rate. When your charisma score is 0, or when Hastur wills it, you become his slavering thrall
* DepartureMeansDeath: Spectral Hunters must stay within 1 mile of the doll that was used in their creation.
* DidYouJustPunchOutCthulhu: Although, this happens very, very rarely, since meeting the aforementioned eldritch abominations usually ends badly. However, 'rarely' does not mean 'impossible', as proved by FanFic/OldManHenderson in his DyingMomentOfAwesome.[[note]](The tale of whom is archived on the 1d4chan wiki [[http://1d4chan.org/wiki/Old_Man_Henderson here]].)[[/note]]
** "Each round 1D3 investigators are scooped up in Cthulhu's flabby claws to die hideously."[[note]]With its MemeticMutation: "Cthulhu eats 1d6 investigators per round. No save."[[/note]]
* DidYouJustRomanceCthulhu: Yog-Sothoth, ''Masks of Nyarlathotep'', ''The Fungi from Yuggoth'' adventure "The Thing in the Well" and the ''Cthulhu Now'' adventure "Love's Lonely Children".
* DisposableVagrant: This procedure is followed by CthulhuMythos cultists in multiple supplements.
* DownInTheDumps: ''Cthulhu Now'' adventure "The Killer Out of Space". A auto junkyard's giant electromagnets can be used to trap a Colour Out of Space.
* DreamLand: The Dreamlands are one of the possible settings of the game.
* EldritchAbomination: Entire bestiaries of 'em.
** HumanoidAbomination: Far less prevalent, but still numerous. Sometimes overlaps with AFormYouAreComfortableWith.
* EmotionSuppression: ''The Asylum and Other Tales'' adventure "The Asylum". Doctor Freygan has developed a drug called Mood Flattener. It temporarily suppresses all emotion in the recipient.
* EvilMask: ''Fragments of Fear'' adventure "Valley of the Four Shrines". A metal mask with Cthulhu's face grants the wearer several powers, but each time it's put on the wearer must make a SAN roll or lose sanity.
* ExplosiveLeash: The Sons of Terror's cranial bombs in ''The Fungi from Yuggoth'' adventure "By the Bay Part II".
* ExpositionOfImmortality: Various campaigns and scenarios hinge on the uncovering of the Mythos and its dabblers alien natures. Key example of this trope in use occurs in the Cthulhu 1990s campaign ''Utati Asfet: The Eye Of Wicked Sight.'' The BigBad, Labib, is actually an immortal from the time of the Pharoahs. Examination of artifacts and documents in his sanctum during the latters stages of the campaign can lead to this conclusion being made by the players.
* ExtraDimensionalShortcut: The setting ''Dreamlands''. The Dreamlands have a number of locations which touch the waking world and allow physical entry from and exit to that world. Some examples are the Enchanted Wood (connects to the Black Forest in Germany, the California redwoods, Transylvania and Roanoke Island), ghoul burrows (Earthly graveyards), the icy lands of Lomar (Alaska, Siberia and Greenland) and certain forbidden ways into the waking world beyond the Tanarian Hills. A daring character could enter the Dreamlands from one of these places in the waking world, travel the Dreamlands to an exit and use it to return to the waking world.
* EyesDoNotBelongThere: Shoggoths in the main rules and proto-shoggoths in the supplement ''The Asylum and Other Tales''.
* TheFace: ''Terror from the Stars'' section "Field Manual of the Theron Marks Society". One {{PC}} should be a Communication Specialist - a charismatic character who is a good talker.
* FailureIsTheOnlyOption. Going insane isn't a matter of "if", it's a matter of "when" and "how soon".
* FamilyEyeResemblance: ''Cthulhu Companion'' adventure "The Secret of Castronegro". The de Diaz and Vilheila-Pereira families have vivid green eyes.
* FictionalColor: The Colours out of Space, The Scepter of Iram in the ''Curse of the Chthonians'' adventure "The City Without A Name", and Sir Aubrey's rocket in ''Masks of Nyarlathotep'' (Shanghai section).
* FlyingBooks: ''Dreamlands'' adventure "The Land of Lost Dreams". While in the title place a {{PC}} can encounter some of these.
* ForensicAccounting: Many early adventures have situations where {{PC}}s can use the Accounting skill to gain information.
* ForgedLetter: ''Shadows of Yog-Sothoth'', adventure "The Coven of Cannich". After the witches (Cthulhu Mythos cultists) in Scotland kill Henry Hancock, they send a fake letter supposedly written by him to his nephew Jacob to cover up his death.
* AFormYouAreComfortableWith: Nyarlathotep, Nodens and Hypnos all exhibit this trope, though for different reasons.
* FortuneTeller: A {{Gypsy}} woman in ''The Fungi from Yuggoth'' adventure "Castle Dark" and Angela Broadmoor in ''Masks of Nyarlathotep'' chapter 3 "Egypt".
* FossilRevival: ''Spawn of Azathoth''. The spell Call Children of Atlach-Nacha can be used to return spider fossils to life.
* FreshClue: ''Terror Australis'' adventure "Old Fella that Bunyip". The Investigators may stumble upon the scene of one of the Bunyip's attacks. They find a picnic site with signs of a struggle and a tea kettle of water heating over a fire. The kettle is still whistling, which means they arrived minutes after the attack.
* FungusHumongous: The ''Terror from the Stars'' adventure "The Temple of the Moon" and the ''Dreamlands'' supplement.
* GameplayAndStorySegregation: It is widely accepted that combat is something to generally be avoided in this game, and that most Mythos entities are unbeatable anyway. However, after about two or three sessions, players will quickly conclude that the best [[DidYouJustPunchOutCthulhu Mythos repellent]] is about six to eight [[MoreDakka Tommy gun]] or [[ShotgunsAreJustBetter 12 gauge shotgun]] wielding JerkAss GeniusBruiser.
* GeneticMemory: ''The Fungi From Yuggoth'' adventure "Sands of Time". Both the archvillain and the player characters experience an awakening of ancient genetic memories stored in their DNA.
* GiantSpider: In the ''Dreamlands'', Leng Spiders can grow to huge size and weigh hundreds of tons.
* GloriousLeader: ''The Fungi from Yuggoth'' campaign. The Brotherhood of the Beast plans to cause worldwide disaster so its leader can step in, save the world and be made President of the U.S. (and eventually ruler of the world).
* GoMadFromTheRevelation: TropeNamer (the phrase is taken from the same paragraph quoted above). When the characters realize just what is going on, their Sanity often snaps. As they learn more about how the world ''really'' works (the "Cthulhu mythos" stat), their maximum Sanity permanently drops by an equal amount. Thus, someone with a perfect Mythos score, having learned everything there is to know about the universe, would have no Sanity at all.
** Well, while a perfect Mythos score is enough to leave you with zero Sanity, it does not mean you know all there is to know (that would still be kinda tempting). Just imagine trying to fill a glass of water (your mindful of sanity) with a truckload of sand. Horrifying, mind-shattering sand...
* GovernmentAgencyOfFiction: Delta Green in the U.S. and PISCES in Britain.
* TheGreys: Featured in DeltaGreen. [[spoiler:They're actually artificial life forms created by the Mi-go as part of their experiments on humanity.]]
* GrimUpNorth: Some campaigns take the [=PC=]s to the Arctic.
* GunAccessories: ''Terror from the Stars'', "Field Manual of the Theron Marks Society". The title Investigator group taped flashlights on top of firearms so they could shoot in the dark.
* GunsAreUseless: Nothing you can lift is high caliber enough to even scratch Cthulhu. Even heavy artillery won't stop him for long. In comparison, Cthuga is a sentient ball of intense heat. Firing soon-to-be blobs of molten metal at him kinda tickles. However, they do a bang-up job on human cultists and low-level Mythos minions, though, so if you find a group planning to call forth either of the above, break out something high caliber.
** "So what happens if you nuke Cthulhu? He reforms ten minutes later, but now he's radioactive!"
* HalfHumanHybrid: The Deep Ones and the various half-human offspring of the Outer Gods.
* HealingFactor: Chthonians, Cthulhu, Hounds of Tindalos, Shoggoths, Shudde M'ell, Star Spawn of Cthulhu and Tsathoggua can all regenerate injuries.
* HighVoltageDeath: supplement The Asylum and Other Tales, adventure "The Asylum". Doctor Freygan's laboratory has a tub into which victims are placed in order to turn them into proto-shoggoths. If a living person is in the tub when the apparatus is activated, electrical bolts slam into their body and instantly (and horribly) kill them by electrocution.
* HollywoodTorches: ''Worlds of Cthulhu'' magazine #3, adventure "The Golden Scorpion".
* {{Hologram}}: The Yithian Communicator in ''The Fungi from Yuggoth''.
* HornAttack: Animals and monsters with butt/gore attacks included the cape buffalo, gnoph-keh and rhino.
* HostileWeather: ''Dreamlands'' adventure "Yellow Sails". The weather report for Sarrub is freezing winds blowing off the sea, bringing blizzards and sleet.
* HotBlade: ''Cthulhu Companion'', adventure "Valley of the Four Shrines". The East shrine is dedicated to Cthugha, a fire deity. A sword found in a secret room can be made to glow yellow-hot.
* HumanAliens: The secretive inhabitants of the subterranean city of K'n-Yan are almost completely indistinguishable from humans.
* HumanSacrifice: If you call a God, you'd best have one handy...
* HydePlaysJekyll: ''The Asylum and Other Tales'' adventure "The Madman". Adam Smythe has a split personality. His evil side pretends to be his normal personality whenever it's in control.
* ImmortalityInducer: Lang Fu's Coat of Life in the ''The Fungi From Yuggoth'', adventure "By the Bay Part I" and Bernardo Diaz's ruby ring in the ''Cthulhu Companion'' adventure "The Secret of Castronegro".
* InstantDeathRadius: Yig's poison kills you instantly if you don't dodge and he hits bare skin. Dholes squash you flat if you don't dodge, regardless of defenses, and any surviving investigators get a roll to see if they find enough of you to bury. Cthulhu doesn't give you a chance to dodge (you're ''really'' not intended to go into combat with any of the above). For obvious reasons, Azathoth and Yog-Sothoth both take this trope UpToEleven. The former, if not properly contained, can and will lay waste to ''entire planets''; the latter has a nasty habit of vaporizing everything in a five-mile radius with ''freaking '''energy bolts'''''.
* JustBeforeTheEnd: Supplement ''Fearful Passages'', adventure "Slow Boat". The far future setting where the [=PCs=] end up, complete with a large orange dying sun and a population of necromancers and zombies.
* KillerGameMaster: A necessity in a game where the dead [=PC=]s are the ''lucky'' ones. However, this does not appear to be the written intent of the game. At least the 5th and 6th edition core rulebooks actually encourage the [[GameMaster Keeper]] to come up with alternatives to simply killing off Investigators, such as having monsters choose to target Non-PlayerCharacters instead, having intelligent monsters avoid stupid direct confrontation, and finding alternative bizarre fates to characters dying outright. On the other hand, despite these recommendations, the fragility of the player characters and the game's attractiveness to a KillerGameMaster are quite real, as is the tendency for protagonists in the material on which the game is based to meet unpleasant endings.
* KillItWithFire: ''Terror from the Stars'', "Field Manual of the Theron Marks Society". An "Indian Water Pump" filled with gasoline can be used as an improvised flamethrower. Spray the monster with gasoline, then set it on fire.
* KidnappedByAnAlly: ''Pursuit to Kadath''. The investigators are kidnapped by a group of armed men and taken to meet U.S. Senator Harold Lindstrom, who wants to hire them to find his son Nils.
* KindRestraints: ''Masks of Nyarlathotep'' adventure "The Derbyshire Murders". Eloise Vane becomes a werewolf on nights with a full moon, so her father and brother lock her away in the castle dungeons then.
* LethalJokeCharacter: [[http://spiritsoffire.com/forum/index.php?topic=3954.0 Who wants to hear the Tale of Old Man Henderson, the character who 'won' Call of Cthulhu?]]
%% http://filesmelt.com/dl/DnD_Henderson2.jpg
* LightningGun: The Mi-go in ''Terror from the Stars'' and ''The Stars Are Right!'' and a Yithian (Great Race) in the ''Fragments of Fear'' adventure "Valley of the Four Shrines".
* LostInTransmission: The Roman legion scribe's account in the ''Cthulhu By Gaslight'' adventure "The Yorkshire Horrors"
* LouisCypher: Nyarlathotep is fond of this. In the ''At Your Door'' campaign, he appears as realtor Atley P. North and a saxophonist called 'the Royal Pant'.
* LuredIntoATrap: ''Shadows of Yog-Sothoth'' adventure "The Worm That Walks". Mr. Edwin sends the {{PC}}s into several situations where they're guaranteed to be attacked.
* MagicIsAMonsterMagnet: ''Cthulhu Companion'' adventure "The Mystery of Loch Feinn". While in the underground area of Castle [=MacLaireag=], any spell casting doubles the chance of a lloigor detecting and attacking the investigators.
* MegaCorp: New World Incorporated in the supplement ''The Fungi From Yuggoth".
* MembershipToken: 'The Asylum and Other Tales'' adventure "The Asylum". Freygan's cultists have recognition symbols: small stones with thongs for wearing around the neck.
* MentalPictureProjector: ''Cthulhu Now'' adventure "Dreams Dark and Deadly". A dream research institute has technology that can read the dreams of sleepers and project them onto TV screens so others can watch them.
* MinorCrimeRevealsMajorPlot: ''Masks of Nyarlathotep''. The murder of author Jackson Elias by cultists leads to a worldwide conspiracy to open a Gate and let the forces of the Cthulhu Mythos conquer the Earth.
* MirrorMonster: ''Dreamlands'' adventure "Lemon Sails". The Temple of the Oracle on Sarrub has a mirror which has been taken over by a wendigo-demon that attacks anyone who tries to use it.
* MistakenForQuake:
** ''Fragments of Fear'' adventure "The Underground Menace". The inhabitants of Winnemuck, Michigan were terrified by a series of earthquakes. Little did they know that the earth tremors were actually caused by a ghoul priest trying to release a CthulhuMythos monster related to the Great Old One Shudde M'ell!
** ''Terror from the Stars'' adventure "The Temple of the Moon". The earthquakes at the archeological dig site are not natural: they're caused when the bottom of the pool inside the Temple slides back to reveal a long shaft downward.
** ''The Fungi from Yuggoth'' adventure "Mountains of the Moon". The earthquakes near the NWI facility in Peru are actually caused by the nearby mining activity of the Mi-go.
* MoralityChip: Inverted in "The Fungi from Yuggoth'' adventure "By the Bay". A MadScientist uses electrical brain implants that can control human beings, to create terrorist criminals and convert a U.S. Treasury agent into TheMole.
* MultiarmedAndDangerous: Many monsters and deities have multiple arms/tentacles, such as Azathoth, Cthugha and Shub-Niggurath.
* MushroomMan: The Fungi from Yuggoth.
* MysteriousAntarctica: ''Beyond the Mountains of Madness'' sends the player characters on an expedition to Antarctica.
* NaughtyBirdwatching: ''The Asylum and Other Tales'' adventure "The Auction". An astronomer has a telescope in his apartment which he uses for his secret hobby, voyeurism.
* NeckSnap: Supplement ''Fearful Passages'', adventure "Sleigh Ride". A giganteus does it to Professor Chance.
* NeverSmileAtACrocodile: The game had all sizes of crocodiles. In the "Valley of the Four Shrines" adventure in "Fragments of Fear" they could be encountered as wandering monsters.
* NoImmortalInertia: Bernardo Diaz in the ''Cthulhu Companion'' adventure "The Secret of Castronegro", Lang Fu in the ''The Fungi from Yuggoth'' adventure "By the Bay Part I" and Omar Shakti in ''Masks of Nyarlathotep'' chapter 3 "Egypt".
* NoSneakAttacks: Encouraged as protocol for the [[GameMaster Keeper]] in the core rulebook. As the [[PlayerCharacter Investigators]] tend to be mere PunyEarthlings, devouring them in their sleep or when they otherwise can't fight back tends to be boring and anticlimactic. Individual pre-written adventure modules may play this straight or avert it, however.
* NowDoItAgainBackwards: The Resurrection spell and the spell used to raise R'lyeh in the ''Shadows of Yog-Sothoth'' adventure "The Rise of R'lyeh".
* OneWingedAngel: Destroying any given one form taken by Nyarlathotep results in his manifesting in his horrifyingly monstrous default shape.
* OnlyShopInTown: Multiple examples
* OperatorIncompatibility: ''Terror from the Stars''. Mi-Go fire their LightningGun by grasping it and altering its electrical resistance. Humans have to clip one of its wires.
* OracularHead: ''The Asylum and Other Tales'', adventure "The Auction". A magical Brass Head could animate and answer questions if it were covered with burning blood.
* OrientExpress: ''Horror on the Orient Express'' is one of the biggest modules published for any roleplaying system.
* OurGhoulsAreCreepier: Ghouls and ghasts, in both the real world and the Dreamlands.
* PartialTransformation: Proto-shoggoths in ''The Asylum and Other Tales'' adventure "The Asylum" and the werewolf Eloise Vane in ''Masks of Nyarlathotep'' chapter 2 "London" adventure "The Derbyshire Monster".
* PhlebotinumOverdose: ''Terror Australis'' adventure "Old Fellow That Bunyip". The investigators must drive a bunyip upriver by calling "Eleanba Wunda", the name of a terrifying spirit which will appear if the name is said too often.
* PitTrap: ''Worlds of Cthulhu'' magazine #3, adventure "The Golden Scorpion".
* PlaceOfProtection: ''Fragments of Fear'', adventure "Valley of the Four Shrines". A path surrounding a lake prevents zombies from passing over it, protecting a human fishing village from them.
* PlanetaryParasite: The boxed set ''Spawn of Azathoth''. If a Seed of Azathoth strikes a planet, it can penetrate it and grow into a Spawn of Azathoth the size of a star. All that's left of the planet is shattered ruins. The former fifth planet of the solar system suffered this fate: its remains are the Asteroid Belt.
* PlayingWithFire: The Great Old One Cthugha and his Fire Vampire servants can perform fire-based attacks.
* PocketProtector: Jack "Brass" Brady's metal plate in the ''Masks of Nyarlathotep'' campaign.
* PortalPicture: Appeared in the ''Dreamlands'' adventure Pickman's Student" and the ''Masks of Nyarlathotep'' adventure "A Serpent in Soho".
* PretenderDiss: ''Cthulhu Companion'', adventure "The Rescue". The werewolf Rafe Pelton despises and maliciously mistreats two insane men who want to be werewolves like him.
* QuicksandSucks: Can be encountered in the jungle in the ''Fragments of Fear'' supplement adventure "Valley of the Four Shrines".
* RapidAging: ''Cthulhu Companion'' adventure "The Secret of Castronegro", ''The Fungi from Yuggoth'' adventure "By the Bay Part I" and the Steal Life spell.
* RedEyesTakeWarning: Multiple examples.
* RegeneratingMana: Characters have a number of magic points equal to their POW score. Casting CthulhuMythos spells uses up the character's magic points. A character regains 1 magic point each (24/POW) hours.
* {{Retcon}}: As of the the fifth edition, the game discards the entire Good vs Evil aspect Derleth tried to jam into the CthulhuMythos, returning to Lovecraft's original vision.
* RiddleMeThis: ''Curse of the Chthonians'' adventure "The City Without A Name". In order to enter, pass through and escape from a special chamber, the investigators must calculate the five numbers of Cthulhu using the occult science of Gematria.
* RightHandAttackDog: ''Masks of Nyarlathotep'', Chapter 5 "Shanghai". Lin Tang-yu's trained pet white gorillas [=TunTun=] and Ping.
* RockOfLimitlessWater: The supplement ''Terror Australis'', adventure "City Beneath The Sands". Power Boy can cause a spring to come out of a rock just by sticking his rangga (ceremonial staff) into it.
* {{Romani}}: ''The Fungi from Yuggoth'' adventure "Castle Dark" and the ''Dark Designs'' adventure "Eyes for the Blind".
* [[SandWorm Really Freaking Huge Sandworm]]: Dholes. As mentioned above, anyone getting in their way is automatically squashed and killed, and the survivors get a roll to try and find enough remains to bury.
* SanityMeter: The TropeMaker.
** Lots of things can cause sanity loss in the game. Increasing Mythos does this, but so do things like killing someone or burning bodies. The game actually has an "Idea" stat, which is a measure of how good your character is at coming up with good ideas. A high idea score is a ''[[DumbIsGood very bad thing]]'', because when you lose too much sanity in one check, your character goes temporarily insane; you can save against that by [[FearlessFool failing an Idea roll]], with a success meaning your character has understood the full implications of what he is seeing.
** Also, increasing your knowledge of the Cthulhu Mythos can not only cost you sanity points during the learning process, but permanently lowers your ''maximum'' Sanity.
* ScoobyDooHoax: In the ''The Asylum and Other Tales'' adventure "Westchester House".
* ScrewDestiny / TakingYouWithMe: [[http://forum.spiritsoffire.com/index.php?topic=3954.0 Old Man Henderson]], the guy who [[DidYouJustPunchOutCthulhu blew up Hastur]].
* SealedEvilInACan: The status of a great many (if not most) of the Great Old Ones, including Cthulhu himself.
* SecretWar: ''Glozel Est Authentique'' adventure "Secrets of the Kremlin''. The Nodens Brotherhood has long opposed a cult that worships Shub-Niggurath.
* SeeTheInvisible: The Powder of Ibn Gazi and special camera lenses in the ''Shadows of Yog-Sothoth'' adventure "Devil's Canyon".
* SeeThruSpecs: ''The Fungi From Yuggoth'' campaign, adventure "The Thing in the Well". A pair of spectacles allows the wearer to see into another dimension. Each time you use them, you could see a monster that could attack and kill you if you don't take them off in time.
* SelfConstructedBeing: ''Dreamlands'' adventure "Pickman's Student". A Great Old One named Ghadamon takes over the body of a human being so he can enter the waking world.
* SelfDestructMechanism: ''TabletopGame/CallOfCthulhu'' campaign ''The Fungi from Yuggoth''. Dr. Dieter's laboratory has one that will destroy the entire installation.
* SingleBiomePlanet: ''Curse of the Chthonians'' adventure "The City Without A Name". If the investigators are very unlucky they can go through a Gate to the home planet of the Chthonians, which is a Volcano Planet.
* ShotgunsAreJustBetter: Also ShortRangeShotgun. Close up, they can deal about 4D6 worth of damage, enough to kill almost anything that isn't ImmuneToBullets. Oh, and short range shotgun can be averted if you load them with rifle rounds.
** Shotguns are one of the most powerful and easily accessible guns on the entire planet. The most practical model listed in the core rule book, the 12 gauge Benelli, has a 7 shot capacity, fires twice per round, and does 4D6/2D6/1D6 (10/20/50 yards). That's a potential of 24 damage, minimal of 4, at point blank range (it's surprisingly rare to fight a battle beyond 20 yards). To put this into perspective; Most games will have three to eight players, each potentially equipped with a boom stick of their own plus side arms and other weapons, concentrating long range fire power into melee monsters with health barely able to sustain a single two-person shotgun volley. Incredibly massive shoggoth? More like incredibly massive Chunky Salsa!
*** In case you were wondering about the math behind this: 4D6 amounts to a minimum of 4 and maximum of 24 damage per shot with 2 shots per turn of combat. 2 x 24 = 48 per player. Assuming all dice rolls go perfectly, 8 players firing simultaneously looks like (2 x 48) 8 = 768 points of damage. The worst possible roll would look like (2 x 4) 8 = 64 points of damage. Assuming average rolls (3.5, the average between the average rolls of 3 and 4), that's 448 points of damage per turn of combat!
* [[ShoutOut/TabletopGames Shout Out]]:
** ''Dark Designs'' adventure "The Menace from Sumatra". Dr. Granger's library has ''The Dynamics of an Asteroid'' from Literature/SherlockHolmes.
** The ''Malleus Monstrorum'' sourcebook derives its name from the German title for the game's ''Creature Companion''. Scott David Aniolowski thought it was such a cool name that he used it for the English sourcebook.
* SickbedSlaying: ''The Fungi From Yuggoth'' adventures "The Dreamer" and "The Worm that Walks".
* SickeningCrunch: Occurs in the ''Fearful Passages'' adventure "Sleigh Ride" and ''The Fungi From Yuggoth'' adventure "Castle Black".
* SmolderingShoes: ''Curse of the Chthonians'' adventure "Dark Carnival". A man is pulled through the iron bars of a gate by ghouls: when his feet get stuck, they're ripped off, leaving them (still inside his shoes) on the ground.
* SoulJar: ''Shadows of Yog-Sothoth'' adventure "Devil's Canyon". The spectral hunters cannot move more than 1 mile away from their kachina dolls, which hold their souls. If a specific chant is conducted over a spectral hunter's doll, it is destroyed.
* SpeakOfTheDevil: ''Terror Australis'' adventure "Old Fella That Bunyip". To drive Bunyip upstream the investigators must say "Eleanba Wunda", the name of a evil spirit which will appear if its name is chanted too often.
* SplitPersonality: ''The Asylum and Other Tales'' adventure "The Madman". An investigator is driven insane by exposure to the Cthulhu Mythos and develops an evil alternate personality.
* SpookySeance: Can occur in both ''The Fungi from Yuggoth'' and ''Pursuit to Kadath''.
* StarfishAliens: The Elder Things actually ''have'' starfish-shaped heads. Then there are the Mi-Go, the Great Race, Cthulhu, etc...
* SufficientlyAdvancedAliens: Most Great Old Ones (and a few species) are described thus, possibly overlapping with outright godhood.
* SummonBiggerFish: ''Terror From The Stars'', "Field Manual of the Theron Marks Society". When facing powerful monsters, summon another deity or monster that hates whatever's attacking you.
* SundialWaypoint: ''Terror from the Stars'' adventure "The Temple of the Moon". In the temple there is a light shaft that allows moonlight to enter, and a pool with a map on the bottom. If the Tablet of the Moon is placed atop the light shaft at midnight under the light of the full moon, the moonlight will be refracted into a bright point of light on the map, showing the location of the main temple of Shub-Niggurath.
* SwordCane: One of the new Victorian Age weapons in ''Cthulhu By Gaslight'' was the sword cane.
* TakingTheBullet: "The Asylum and Other Tales" adventure "The Mauritania". Bodyguards have the skill Block, which allows them to hurl their body in between an attacker and the person they're protecting.
* TapOnTheHead: ''The Asylum and Other Tales'', adventure "The Asylum". Dr. Freygan's neck pinch. Also, typical of a "Knockout" attack.
* TarotMotifs: A {{Gypsy}} FortuneTeller uses Tarot cards in ''The Fungi from Yuggoth'' campaign, section "Castle Dark"
* TearOffYourFace: In ''Terror Australis'', the Mimi are creatures from Australian Aboriginal {{mythology}}. When angry at a human they may eat all the flesh from his face, leaving the victim alive but horrendously disfigured.
* ThankYourPrey: ''Terror Australis'' adventure "City Beneath The Sands''. Power Boy could call animals and ask that they allow themselves to be eaten. If they agreed, he praised their beauty and courage.
* ThatWasTheLastEntry: Multiple examples
* TheseAreThingsManWasNotMeantToKnow: Disregard this warning at your own risk.
* ThisIsAsFarAsIGo: ''Fragments of Fear'' adventure "Valley of the Four Shrines". When the party reaches the cave that leads to the Valley, any native porters hired from nearby areas refuse to enter.
* ThisWasHisTrueForm: Philip Boucher in the ''Shadows of Yog-Sothoth'' adventure "The Warren" and Eloise Vane in the ''Masks of Nyarlathotep'' chapter 2 "London" adventure "The Derbyshire Monster".
* ThoseWackyNazis: The Church of a Thousand Tomorrows from the Monograph "The Big Book of Cults". Also overlaps with StupidJetpackHitler.
* ThrillerOnTheExpress: Both ''Horror on the Orient Express'' and the "The Iron Ghost" adventure in ''Fearful Passages'' have train-based adventures.
* TickleTorture: A nightgaunt can grab people and tickle them, rendering them helpless so it can carry them away.
* TomeOfEldritchLore: Characters may be given the opportunity to read the Necronomicon and other cursed books, at high cost to their Sanity.
* TooManyMouths: ''Dreamlands'' supplement. The Maws of Pandemonium spell caused the victim's body to sprout a red-lipped mouth that gibbered and moaned as it drained the victim's magic points.
* TheTopicOfCancer: ''The Asylum and Other Tales'' adventure "The Asylum". One of Dr. Freygan's drugs is Cellular Accelerator, which can cause cancer throughout the recipient's body.
* TorchesAndPitchforks: ''Worlds of Cthulhu'' #3, adventure "Malevolence".
* TotalPartyKill: A definite possibility in case of failure. Even when things don't go disastrously wrong, a high character attrition rate is to be expected. Some players believe that the TotalPartyKill is what happens if you're ''lucky.'' If you're ''un''lucky? AFateWorseThanDeath.
* TownWithADarkSecret: The small Vermont town of Bensamin in the ''Dreamlands'' adventure "To Sleep, Perchance to Dream".
* TrashcanBonfire: ''Fearful Passages'' adventure "The Iron Ghost". There's one in the 1934 Southern Pacific car.
* TheTunguskaEvent: The main rules hint that Azathoth was involved. ''Spawn of Azathoth'' says that it was caused by a Seed of Azathoth entering the Earth's atmosphere.
* TropeCodifier: For a fair number of CosmicHorror tropes, sometimes literally just by virtue of wrapping concrete game rules around things that the literary source material only obliquely hints at.
* TwoHalvesMakeAPlot: In the supplement ''Terror from the Stars'', adventure "The Temple of the Moon". The [[PlayerCharacter Player Characters]] and two independent villains each receive 1/3 of the Tablet of the Moon, a piece of gold jewelry that allows the user to find the location of a treasure on a map. The players must either defeat one or both villains and take their pieces or team up with them.
* UndeadTaxExemption: ''The Fungi from Yuggoth'', adventure "Castle Dark". Baron Hauptmann transfers his mind into a new body every few decades and assumes the victim's identity.
* UnexpectedInheritance: ''The Asylum and Other Tales'' adventure "Black Devil Mountain". A {{PC}}'s brother dies and leaves them some property which has CthulhuMythos activity going on nearby.
* UsingYouAllAlong: ''Curse of the Chthonians'' adventure "The Curse of Chaugnar Faugn". The investigators are manipulated into helping a mad professor awaken the title CthulhuMythos deity from its statue form.
* VampireVannabe: ''Cthulhu Companion'', adventure "The Rescue". Jocko wants to become a werewolf like Rafe Pelton. Pelton lies to him and cruelly makes him perform useless humiliating acts.
* VampiricDraining: Byakhee, chthonians, Dark Young of Shub-Niggurath, Shub-Niggurath and star vampires can all drain bodily fluids and/or blood. In early editions regular vampires could as well. Tsathoggua can drain points of Characteristics (Strength, Dexterity, etc.).
* WeakenedByTheLight: Fog-Spawn, Hunting Horrors, Vampires, Nyarlathotep in his "Haunter of the Dark" form, Servants of Glaaki, Dreamland shades and others.
* WhenTheClockStrikesTwelve: Multiple examples.
* WithGreatPowerComesGreatInsanity: For those who mess with magic. Dragon Magazine once said that ''Call of Cthulhu'' is the only RPG where ''no one'' wants the magic item loot.
* TheWormThatWalks: The name first appeared in the Shadows of Yog-Sothoth adventure "The Worm That Walks" as the name of a monster that was '''not''' made out of worms. An example called "the Crawling One" appeared in the ''Shadows of Yog-Sothoth'' adventure "The Watchers of Easter Island".
* WretchedHive: Dylath-Leen in the ''Dreamlands'' supplement.
* YouCannotGraspTheTrueForm: In their vanishingly rare moments of kindness, Outer Gods may manifest in forms not conducive to Sanity-blasting shock. Or, in the case of Nyarlathotep, it's just another way for them to mess with human minds.
* YowiesAndBunyipsAndDropBearsOhMy: ''Terror Australis'' has statistics for quite a few mythological Australian monsters, including the yowie and bunyip.

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