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We would like to dedicate this tome to our spouses and families who tirelessly supported us during its writing and development. And to he who must not be named.

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CreditsAuthors

Sandy Petersen, James Jacobs, Arthur Petersen, Ian Starcher, David N. Ross

Development AnD Conversion

David N. Ross

projeCt DireCtor

Arthur Petersen

Business mAnAger

Christine Graham

eDiting AnD proofreADing

Eytan Bernstein, Erik Scott de Bie, Thomas Weber

Cover AnD interior Art

Kent Hamilton

monster AnD greAt olD one Art

Helge Balzer

ADDitionAl Art

Richard Luong

grAphiC Design AnD lAyout

Tony Mastrangeli

sAles mAnAger

Christopher Helton

shipping

Christy Crace

Customer support

George Botelho

Community AnD vf support

Pierre “Pit” Lanrezac

plAytest support

Lincoln Petersen, Andrew Lucio, Jonathan Cohen, Ryan Brown

Sandy Petersen’s Cthulhu Mythos, © 2018, Petersen Games.Printed in China.ISBN-13: 978-0-9995390-4-0

Product Identity: The following items are hereby identified as Product Identity, as defined in the Open Game License version 1.0a, Section 1(e), and are not Open Content: All trademarks, registered trademarks, dialogue, plots, storylines, locations, characters, artwork, and trade dress. (Elements that have previously been designated as Open Game Content or are in the public domain are not included in this declaration.)

Open Content: Except for material designated as Product Identity (see above), the game mechanics of this Petersen Games game product are Open Game Content, as defined in the Open Gaming License version 1.0a Section 1(d). No portion of this work other than the material designated as Open Game Content may be reproduced in any form without written permission.

No part of this book or contents were plagiarized from the Necronomicon of Abdul Alhazred, and no foul entities from the spheres beyond will be summoned during the use of this book. However, if such an untoward event were to happen upon reading the contents of this book, Petersen Games advises that the proper ritual precautions be taken, including but not limited to the inscription of an Elder Sign upon your door or gate.

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ChApter 1: using this Book . . . . . . . 1WhAt is the Cthulhu mythos? . . . . . . . . . . 1Bringing horror to heroiC fAntAsy . . . . . 2

ChApter 2: mythos plAyer ChArACter rACes . . . . . . . . . . . . . . .7DreAmlAnDs CAt . . . . . . . . . . . . . . . . . . . . . 8ghoul . . . . . . . . . . . . . . . . . . . . . . . . . . . 14gnorri . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Zoog . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28otherWorlDly humAns . . . . . . . . . . . . . . . 34

ChApter 3: plAyer ChArACter options . . . . . . . . . . . . . . . . . . . . .37ClAss options for mythos rACes . . . . . . . 37

Dreamlands Cat . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Ghoul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Gnorri . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Zoog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

other ClAss options . . . . . . . . . . . . . . . . 43Barbarian Primal Path . . . . . . . . . . . . . . . . . . . . . . 43Bardic College . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Cleric Divine Domains . . . . . . . . . . . . . . . . . . . . . . 45Druid Circles . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Fighter Martial Archetype . . . . . . . . . . . . . . . . . . . . 51Paladin Oath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Roguish Archetypes . . . . . . . . . . . . . . . . . . . . . . . . 53Trapsetter Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Sorcerous Origins . . . . . . . . . . . . . . . . . . . . . . . . . 55Warlock Options . . . . . . . . . . . . . . . . . . . . . . . . . . 57Wizard Arcane Tradition . . . . . . . . . . . . . . . . . . . . . 61

BACkgrounDs . . . . . . . . . . . . . . . . . . . . . . 62Alienist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Mythos Cultist . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Mythos Survivor . . . . . . . . . . . . . . . . . . . . . . . . . . .64Visionary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

neW feAts . . . . . . . . . . . . . . . . . . . . . . . . . 67

ChApter 4: insAnity AnD DreAD . . . . . . . . . . . . . . . . . . .70DreAD AnD insAnity . . . . . . . . . . . . . . . . . 71

Dread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72Insanity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

iA! iA! Cthulhu fhtAgn: An Aklo primer . . . . . . . . . . . . . . . . . . . . 81the DreAmlAnDs . . . . . . . . . . . . . . . . . . . 81

Normal Dreaming . . . . . . . . . . . . . . . . . . . . . . . . . 81Dreamlands Travel . . . . . . . . . . . . . . . . . . . . . . . . . 82

ChApter 5: spellCAsting in the mythos . . . . . . . . . . . . . . . . . .85formulAs . . . . . . . . . . . . . . . . . . . . . . . . . 85spells . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Spell List Not Required. . . . . . . . . . . . . . . . . . . . . .88Class Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Spell Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . 92

ChApter 6: mythos items AnD texts . . . . . . . . . . . . . . 119ADventuring geAr . . . . . . . . . . . . . . . . . 119Alien teChnology AnD mAgiC items . . . . 122texts of the Cthulhu mythos . . . . . . . . 132

Text Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . 133

ChApter 7: Cults of the mythos . . . . . . . . . . . . . . . . . 139Cult of the BlACk goAt . . . . . . . . . . . . . 140Cult of the CrAWling ChAos . . . . . . . . . 141

Coven of the Black Man . . . . . . . . . . . . . . . . . . . . 141Cult of the Haunter . . . . . . . . . . . . . . . . . . . . . . . 142Cult of the Howler . . . . . . . . . . . . . . . . . . . . . . . . 142Cult of the Shadow Pharaoh . . . . . . . . . . . . . . . . . 143Retinue of the Bloated Woman . . . . . . . . . . . . . . . 143Seekers of the Dark Demon . . . . . . . . . . . . . . . . . . 143

Cult of greAt Cthulhu . . . . . . . . . . . . . 144CultiC mADness of the nuCleAr ChAos . 145Cult of the opener of the WAy . . . . . . . 146Cult of the sleeper . . . . . . . . . . . . . . . . 147Cult of the WinDWAlker . . . . . . . . . . . . . 149Cult of the yelloW sign . . . . . . . . . . . . 150lesser Cults . . . . . . . . . . . . . . . . . . . . . 152

Cult of Abhoth . . . . . . . . . . . . . . . . . . . . . . . . . . . 152Cult of Atlach-Nacha . . . . . . . . . . . . . . . . . . . . . . 152Cult of the Water Lizard . . . . . . . . . . . . . . . . . . . . 152Cult of Byatis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152Cult of Chaugnar Faugn . . . . . . . . . . . . . . . . . . . . 153Cult of Cthugha . . . . . . . . . . . . . . . . . . . . . . . . . . 153Cult of Father Dagon and Mother Hydra . . . . . . . . 153Cult of Ghatanothoa . . . . . . . . . . . . . . . . . . . . . . . 154Cult of Nyogtha . . . . . . . . . . . . . . . . . . . . . . . . . . 154Cult of the Green Flame . . . . . . . . . . . . . . . . . . . . 154Cult of Yig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

tCho-tCho Culture . . . . . . . . . . . . . . . . 155Deep one Culture . . . . . . . . . . . . . . . . . 156mythos entities AnD religion . . . . . . . . 157

Deep Ones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158Ghouls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158Fungi from Yuggoth . . . . . . . . . . . . . . . . . . . . . . . 158Elder Things and the Great Race of Yith. . . . . . . . . 158Moon-beasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

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Other Aliens . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

other rACes AnD the mythos . . . . . . . . 158Dragonborn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158Dwarves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158Elves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Gnomes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Goblinoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Halflings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Humans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Kobolds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Lizardfolk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Merfolk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Orcs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Tieflings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

ChApter 8: greAt olD ones, outer goDs, AnD others . . . . . . . 161reADing An elDer influenCe stAt BloCk . . . . . . . . . . . . . . . . . . . . . . . 162ABhoth . . . . . . . . . . . . . . . . . . . . . . . . . 165

The Filth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

AtlACh-nAChA . . . . . . . . . . . . . . . . . . . . 168Avatar of Atlach-Nacha . . . . . . . . . . . . . . . . . . . . . 170

AZAthoth, the DAemon sultAn . . . . . . . . .171Bokrug, the WAter liZArD . . . . . . . . . . . 174

The Ghosts of Ib . . . . . . . . . . . . . . . . . . . . . . . . . 176Avatar of Bokrug . . . . . . . . . . . . . . . . . . . . . . . . . 177

ByAtis, the serpent-BeArDeD . . . . . . . . 178Avatar of Byatis . . . . . . . . . . . . . . . . . . . . . . . . . . 180

ChAugnAr fAugn . . . . . . . . . . . . . . . . . . 181Avatar of Chaugnar Faugn . . . . . . . . . . . . . . . . . . . 182Scion of Chaugnar Faugn . . . . . . . . . . . . . . . . . . . 183

CthughA . . . . . . . . . . . . . . . . . . . . . . . . 184fAther DAgon . . . . . . . . . . . . . . . . . . . . 188

Father Dagon . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

ghAtAnothoA . . . . . . . . . . . . . . . . . . . . . 191Rootling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

ghroth, the hArBinger . . . . . . . . . . . . . 196Worm of Ghroth . . . . . . . . . . . . . . . . . . . . . . . . . 199

goBogeg, the moon lADDer . . . . . . . . . .200greAt Cthulhu . . . . . . . . . . . . . . . . . . . 204hAstur the unspeAkABle . . . . . . . . . . . . 209ithAquA . . . . . . . . . . . . . . . . . . . . . . . . . 214the king in yelloW . . . . . . . . . . . . . . . . 221

The King in Yellow. . . . . . . . . . . . . . . . . . . . . . . . 224

mother hyDrA . . . . . . . . . . . . . . . . . . . . 225Mother Hydra . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

nyArlAthotep, the CrAWling ChAos . . . . 228The Bloated Woman . . . . . . . . . . . . . . . . . . . . . . .230The Dark Demon . . . . . . . . . . . . . . . . . . . . . . . . . 232The Haunter of the Dark . . . . . . . . . . . . . . . . . . . . 234The Howler in Darkness . . . . . . . . . . . . . . . . . . . . 237The Shadow Pharaoh . . . . . . . . . . . . . . . . . . . . . . 238

nyogthA . . . . . . . . . . . . . . . . . . . . . . . . . 240Nyogtha Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

quAChil uttAus . . . . . . . . . . . . . . . . . . . 244rhAn-tegoth . . . . . . . . . . . . . . . . . . . . . 249

Rhan-Tegoth . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252

shuB-niggurAth . . . . . . . . . . . . . . . . . . . 253tsAthogguA, fAther of formless spAWn . 259

Avatar of Tsathoggua . . . . . . . . . . . . . . . . . . . . . . . 261

tulZsChA . . . . . . . . . . . . . . . . . . . . . . . . 262uBBo-sAthlA, the tome keeper . . . . . . . 264yig, fAther of snAkes . . . . . . . . . . . . . . 269

Avatar of Yig . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

yog-sothoth . . . . . . . . . . . . . . . . . . . . . 272

ChApter 9: mythos monsters . . . 277AByssAl CustoDiAn . . . . . . . . . . . . . . . . . 278Bhole . . . . . . . . . . . . . . . . . . . . . . . . . . . 281

Bhole Hatchling . . . . . . . . . . . . . . . . . . . . . . . . . . 281Adult Bhole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282

BrAin CylinDer . . . . . . . . . . . . . . . . . . . 283Scholar Brain Cylinder . . . . . . . . . . . . . . . . . . . . . 284Sorcerer Brain Cylinder . . . . . . . . . . . . . . . . . . . . 284Control Drone . . . . . . . . . . . . . . . . . . . . . . . . . . . 286

ByAkhee . . . . . . . . . . . . . . . . . . . . . . . . . 287CAt, DreAmlAnDs . . . . . . . . . . . . . . . . . . 288

Dreamlands Cat, Saturnian . . . . . . . . . . . . . . . . . . 288Dreamlands Cat, Uranian . . . . . . . . . . . . . . . . . . . 289Ulthar Champion . . . . . . . . . . . . . . . . . . . . . . . . .290

Colour out of spACe . . . . . . . . . . . . . . . 291DArk young of shuB-niggurAth . . . . . . 293

Adolescent Dark Young . . . . . . . . . . . . . . . . . . . . . 293Adult Dark Young . . . . . . . . . . . . . . . . . . . . . . . . . 294Mature Dark Young . . . . . . . . . . . . . . . . . . . . . . . 295

Deep one . . . . . . . . . . . . . . . . . . . . . . . . 296Deep One Bishop . . . . . . . . . . . . . . . . . . . . . . . . . 297Deep One Hybrid Cultist . . . . . . . . . . . . . . . . . . . 298Deep One Scion Priest of Cthulhu . . . . . . . . . . . . . 299

Dhole . . . . . . . . . . . . . . . . . . . . . . . . . . 300Dhole Hatchling . . . . . . . . . . . . . . . . . . . . . . . . . . 301Dhole Adult . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302

DimensionAl shAmBler . . . . . . . . . . . . . . 304elDer thing . . . . . . . . . . . . . . . . . . . . . . 306eremite (mythos WiZArD) . . . . . . . . . . . . 309

Eremite Symbiont . . . . . . . . . . . . . . . . . . . . . . . . 310Dracoform Eremite Symbiont . . . . . . . . . . . . . . . . 310Dracoform-Bound Eremite . . . . . . . . . . . . . . . . . . 311

eye of the WAtCher . . . . . . . . . . . . . . . . 312fAvoreD one of nyArlAthotep (million fAvoreD ones) . . . . . . . . . . . . . 314fire vAmpire . . . . . . . . . . . . . . . . . . . . . . 315flying polyp . . . . . . . . . . . . . . . . . . . . . . 317formless spAWn . . . . . . . . . . . . . . . . . . . 320ghAst, mythos . . . . . . . . . . . . . . . . . . . . 323ghoul, mythos . . . . . . . . . . . . . . . . . . . 324

Crypt Lurker . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325Charnel Whisperer . . . . . . . . . . . . . . . . . . . . . . . . 326

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Grave Sage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

gnoph-keh . . . . . . . . . . . . . . . . . . . . . . 328gnorri . . . . . . . . . . . . . . . . . . . . . . . . . . 330gug . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332hounD of tinDAlos . . . . . . . . . . . . . . . . 334hunting horror . . . . . . . . . . . . . . . . . . 336leng folk . . . . . . . . . . . . . . . . . . . . . . . 338

Leng Folk Thief . . . . . . . . . . . . . . . . . . . . . . . . . . 339Leng Necromancer . . . . . . . . . . . . . . . . . . . . . . . . 339

leng spiDer . . . . . . . . . . . . . . . . . . . . . . 341Web Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341Old Leng Spider . . . . . . . . . . . . . . . . . . . . . . . . . 343

mi-go, the fungi from yuggoth . . . . . . 344Mi-go Scout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345Mi-go Warrior . . . . . . . . . . . . . . . . . . . . . . . . . . . 345Mi-go Dimension Walker . . . . . . . . . . . . . . . . . . . 346

moon-BeAst . . . . . . . . . . . . . . . . . . . . . . 347Moon-priest of Nyarlathotep . . . . . . . . . . . . . . . . . 348Moon-vassal of Nyarlathotep . . . . . . . . . . . . . . . . . 349

nightgAunt . . . . . . . . . . . . . . . . . . . . . . 350outer mutAnt, ABominAtion, AnD spAWn . . 351

Outer Mutant Scout . . . . . . . . . . . . . . . . . . . . . . . 352Outer Mutant Priest of Yog-sothoth . . . . . . . . . . . . 353Thrall of Yog-Sothoth . . . . . . . . . . . . . . . . . . . . . 353Outer Abomination . . . . . . . . . . . . . . . . . . . . . . . 354Outer Spawn . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356

re-AnimAteD . . . . . . . . . . . . . . . . . . . . . . 359Re-animated Laborer . . . . . . . . . . . . . . . . . . . . . . 359Re-animated Guard . . . . . . . . . . . . . . . . . . . . . . .360Re-animated Raider . . . . . . . . . . . . . . . . . . . . . . .360

sAtyr, mythos . . . . . . . . . . . . . . . . . . . . 361High Priest of Shub-Niggurath . . . . . . . . . . . . . . . 362

serpentfolk . . . . . . . . . . . . . . . . . . . . . . 364Serpentfolk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365Serpentfolk Alchemist . . . . . . . . . . . . . . . . . . . . . 365

servitor of the outer goDs . . . . . . . . . 366shAntAk . . . . . . . . . . . . . . . . . . . . . . . . . 368shoggoth . . . . . . . . . . . . . . . . . . . . . . . . 370shoggoth, proto- . . . . . . . . . . . . . . . . . 372shuB-niggurAth, DAughter of . . . . . . . . 375slime molD . . . . . . . . . . . . . . . . . . . . . . 377

Slime Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378Immature Slime Mold . . . . . . . . . . . . . . . . . . . . . . 378

stAr vAmpire . . . . . . . . . . . . . . . . . . . . . 379stArspAWn . . . . . . . . . . . . . . . . . . . . . . . . 380

Larval Starspawn . . . . . . . . . . . . . . . . . . . . . . . . . 381

tCho-tCho . . . . . . . . . . . . . . . . . . . . . . . 384Okkator Assassin . . . . . . . . . . . . . . . . . . . . . . . . . 384Masked Okkator . . . . . . . . . . . . . . . . . . . . . . . . . . 385

un-mAn . . . . . . . . . . . . . . . . . . . . . . . . . . 387unDeAD, mythos . . . . . . . . . . . . . . . . . . 388

Yellow Sign Attendant. . . . . . . . . . . . . . . . . . . . . . 389Deathless Wizard . . . . . . . . . . . . . . . . . . . . . . . . . 389Risen Warlock . . . . . . . . . . . . . . . . . . . . . . . . . . .390

voonith . . . . . . . . . . . . . . . . . . . . . . . . . 391 WAmp . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 WenDigo . . . . . . . . . . . . . . . . . . . . . . . . . 394

Ravenous Wendigo . . . . . . . . . . . . . . . . . . . . . . . . 394Windwalker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396

yith, greAt rACe of . . . . . . . . . . . . . . . . 397Past Yithian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398Future Yithian . . . . . . . . . . . . . . . . . . . . . . . . . . . 399

yothAns . . . . . . . . . . . . . . . . . . . . . . . . .400Yothan Warrior . . . . . . . . . . . . . . . . . . . . . . . . . . 401Yothan Designer . . . . . . . . . . . . . . . . . . . . . . . . . . 401Yothan Commander . . . . . . . . . . . . . . . . . . . . . . .402Draconic Amalgam . . . . . . . . . . . . . . . . . . . . . . . .402

Zoog . . . . . . . . . . . . . . . . . . . . . . . . . . . 403Grove Keeper . . . . . . . . . . . . . . . . . . . . . . . . . . .403Zoog Trapper . . . . . . . . . . . . . . . . . . . . . . . . . . . .403

AppenDix 1: nonplAyer ChArACters . . . . . 404Blessed Berserker . . . . . . . . . . . . . . . . . . . . . . . . .404Cult Killer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .404Cult Mastermind . . . . . . . . . . . . . . . . . . . . . . . . .405Obsessed Artist . . . . . . . . . . . . . . . . . . . . . . . . . .406Urbane Magician . . . . . . . . . . . . . . . . . . . . . . . . .406Witch of the Woods . . . . . . . . . . . . . . . . . . . . . . . .407

AppenDix 2: enCounter tABles . . . . . . . . 408Aliens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .408Ancient Past . . . . . . . . . . . . . . . . . . . . . . . . . . . . .409Dreamlands and Plateau . . . . . . . . . . . . . . . . . . . . 410Hill Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411Poles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412Sea and Coast . . . . . . . . . . . . . . . . . . . . . . . . . . . 414Underground . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415Urban Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

generAl inDex . . . . . . . . . . . . . . . 419monsters By ChAllenge rAting . 422items/ArtifACts . . . . . . . . . . . . . 424

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1Using this Book

This book provides rules for both players and game masters (GMs) to incorporate elements of the venerable Cthulhu Mythos into the fifth edition of the world’s most famous classic fantasy roleplaying game. Inside, you will find tips on how to run fantasy horror games, rules for new playable races, options to customize player charac-ters’ class features for cosmic horror games, new rules for dread and insanity in the cosmic horror tradition, new spells, including a new subtype of spells called formulas that even non-spellcasters can cast with some risk, new items and artifacts, and more.

Players will find the most use in the races, class options, dread and insanity rules, spells, and items (with the exception of some spells, rituals, and items linked directly to Great Old Ones and Outer Gods). Chapter 3 includes new feats and a new skill, Yog-Sothothery, which can be used for most matters covered in this book but strains the sanity of those who delve into matters beyond normal mor-tal comprehension. Chapter 4 contains rules for dread, insanity, and the extradimensional Dreamlands that work with the standard game rules and evoke the feel of cosmic horror.

In the second part of the book, GMs will find new tools for challenging player characters, including descriptions of many dangerous cults and their tactics, rules for facing the overwhelming power of Great Old Ones and Outer Gods directly, and dozens of horrific monsters. All these rules are generally useful for building antagonists in any campaign, but they are especially appropriate for a game that involves the Mythos to some degree. All the rules in this book can be used with just the core books.

What is the Cthulhu Mythos?In the 1920s and 1930s, an obscure American writer named H. P. Lovecraft penned some of the most inventive and evocative horror tales ever written. He broached top-ics never before conceived, devised a multitude of terrify-ing entities, and invented a whole new approach to horror, changing the face of fantastic fiction forever.

Yet he did even more. He was active in the Amateur Press Association of his time and corresponded heavily with other authors, giving them advice and mentoring them. One of his innovations was to create a sort of com-mon mythology, which multiple authors would draw upon when writing horror tales. Most infamously, he created the fearful book the Necronomicon, which was mentioned by dozens of other writers, giving it an aura of realism that is rare in fiction. The same is true for many of his other creations.

The framework he invented is usually called the Cthulhu Mythos, named after one of his most famous frights. And here we are today, steeping ourselves again in its awesome and terrible secrets.

The Cthulhu Mythos is based on the principle that humanity is not the center of the universe. The cosmos is vast and filled with unthinkable forces, many not subject to our own natural laws. Some of these forces are unthink-ably powerful—best considered to be like unto gods. These include Great Old Ones and Outer Gods such as Yog-So-thoth, Azathoth, Hastur, and Cthulhu. Others are lesser beings, though still fearsome and dangerously intelligent, such as the fungi from Yuggoth, the deep ones, or the elder things. These forces can manifest in the physical world as well, giving supernatural potency to inanimate objects or even concepts, such as geometry and mathematics.

The Mythos is nothing if not scientific, though humanity does not and indeed cannot know everything. The magic of the Mythos is all founded upon scientific principles, discovered or undiscovered.

Come, let us explore Lovecraft’s dire imagination together.

—Sandy Petersen

Searchers after horror haunt strange, far places.

—H. P. Lovecraft, “The Picture in the House”

Chapter 1: Using This Book

Sandy’s NotesHere and there, Sandy’s Notes present direct advice from Sandy Petersen to GMs regarding how to use these rules elements in a game or how to describe them to players.Sam

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2 Using this Book

Bringing Horror to Heroic Fantasy

With Sandy Petersen

Three Basic rules of horrorM. R. James was a writer in the early 20th century whospecialized in creepy ghost stories. One of Lovecraft’sfavorite authors, James wrote an essay in which he laid outthree rules to construct an effective ghost story. His rulesapply to any type of horror, however, and I consciouslyapply them to scenario-building and when running hor-ror-themed games.

The firsT rule: Don’T use Jargon

Nothing spoils the sense of fear more than bringing the player out of the game and back into real life. Every time you refer specifically to game rules or introduce concepts by means of technical terminology, you lose a bit of poten-tial creepiness. The game is filled with tactical options, all of which use precise terms, which means you, the game master, need to find ways to avoid saying things like, “Let’s see… the shoggoth acts on initiative count 21. It rolls and hits with an… er… pseudopod attack, inflicting 3d10+9 bludgeoning damage, plus 2d6 acid. What’s your Constitu-tion save bonus?”

Don’t articulate monsters’ actions, but instead do the rolls, avoiding overmuch commentary. You still need to inform the players of damage inflicted and special restrictions, but you can accomplish this without parroting specific game rules. Use evocative descriptions, like “the creature moves with sickening speed, lashing out a tendril dripping with hissing acid.” Experienced game masters may already be doing this—it is one of the basics of draw-ing players into an adventure.

The seconD rule: Make The eneMy Malign

Friendly ghosts aren’t scary—it’s a fact of life. This applies to monstrous forces too. If the players find out that the fungi from Yuggoth are trying to establish a quiet mining base, all terror of them vanishes. The Mythos is full of entities that players can interact with, but all of them are malign and creepy, even the sometimes-peaceful ones. You can learn the language of ghouls, but even when they are friendly, they are always eyeing your physique with an eye to how tasty you look. Even the small and seemingly harm-less zoogs gleefully trap and eat visitors to their forest.

Fortunately, the Mythos is filled with terrifying purpose. Sure, the fungi from Yuggoth might only say they want a quiet mining base, but there must be more to it than that. What are they mining? What is their underlying purpose? Are they using the ore to construct some sort of gigantic bio-techno-magical device? If so, what will it do?

At first glance, the great race of Yith appears respectably neutral—even benign. That is, until you realize that they periodically exterminate entire sentient species by mass

mind-swap to continue their existence! (Humanity has only escaped this fate because it is too puny for Yithian ambition. Thus far.)

The ThirD rule: use a MunDane seTTing

James points out if you set a ghost story in an esoteric and inaccessible locale, readers can’t easily imagine them-selves in that situation. As a result, he set all of his stories in the places and locales he knew well: seaside hotels, old country churches, public libraries, and so forth.

You have a major advantage here, since you are running a roleplaying game. Your players normally throw them-selves into the roles of their characters, empathizing with them and cross-exchanging personality traits. As a result, they know and feel their characters, and it’s easy for them to buy into the setting you choose.

You can make the story even more dangerous by putting it right in the heart of the players’ stomping grounds. You could set up an adventure with a shoggoth as a dangerous enemy under a distant glacier, but the players will be more invested if you have that same shoggoth patrolling the sewers under your campaign’s capital city, sneaking up through openings and pulling victims down to feed. Know-ing that shoggoths exist in some distant place in the world is one thing. Knowing that there is a shoggoth in your home city eating folks every night is another thing entirely.

aDDing horror To aDvenTuresHorror is a delicate topic. When horror is combined with another genre, the usual result is that the other genre wins out. For example, most horror-comedies are really just comedies with a horror element. Many attempts have been made to mix horror and superheroes, and, again, the end result is generally a superhero story with a horror element. Most players of fantasy roleplaying games under-standably are focused on high adventure, derring-do, and sword and sorcery. And of course, when horror is added to the adventure theme, just as with other genres, the adven-ture is what remains, though now horror-tinged.

This is not necessarily a bad thing. Consider the dif-ference between the films Alien and Aliens. The first is a horror movie. The second is an adventure movie with horror elements. Both are great films.

If you just want new enemies for your players to battle and investigate, this book has everything you need, with a variety of interesting creatures you can pull out of your back pocket to surprise and intrigue your players. Almost all of these entities have their own little tricks and traps to spring on the players. They range in power from the easi-ly-defeated (zoogs, ghouls, etc.) to the almost unstoppable (flying polyps, starspawn, etc.) to truly awful impossibili-ties that will drive the hardiest adventurer mad (Hastur, Azathoth, etc.).

The fact is that Lovecraft’s monsters aren’t just mon-sters. They have personalities. And as such, you can use them for much more than just bags of hit points. Most obviously, they need not always be treated as enemies. Yes, these monsters can be malign, cannibalistic horrors, but

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they are most often intelligent horrors who are able to understand and sometimes collaborate with humans. They have purposes. For example, on a lonely road, the player characters arrive at an inn run by zoogs. This simple premise is alight with possibilities. What would the zoogs want as payment? What do they offer in exchange, beyond sleeping quar-ters and a fine meal of moonberry wine and rat-on-a-stick? The zoogs could have a gift shop, consisting of goods taken from people foolish enough to sleep alone and unguarded in the zoogs’ rooms. (After all, they are still zoogs.)

Even more horrendous mon-sters may be able to interact with an adventuring party outside of mere combat. The fungi from Yuggoth maintain a secret soci-ety of people who do the fungi’s will in return for technological and biological wonders. The fungi actively evangelize for this society, and the most useful people for their purposes are, clearly, adventurers: itinerant and well-traveled, generally individually powerful, and highly experienced. For all these reasons, they make excellent agents. While your own group of adventurers are, no doubt, un-willing to serve the terrible goals of the fungi, a rival party might not be so high-minded, presenting an excellent threat for the players to encounter. That they serve the fungi would not be immediately obvious, but perceptive adventurers will invariably notice signs of Yuggoth’s control…

As you look through the monsters and other elements of this book, consider many such possible uses, both obvious and subtle. You can certainly use any adventure or situa-tion you like, merely plugging in the Lovecraf-tian entities as appropriate. But for a memorable and compelling game, spend some planning time considering how the involvement of the Mythos changes the situation.

Most players are familiar with the classic dun-geon crawl, commonly constructed by an insanely powerful lich or a mad wizard, making it a good starting structure for a game. Perhaps the dun-geon is instead being run by a Lovecraftian entity of enormous power. I’ll randomly select a possibility (rolls dice); okay, I came up with Nyarlathotep. Arbitrarily I’ve named this dungeon “The Twisted Pyramid.” (Seems Egyptian-ish.)

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Now obviously the Crawling Chaos has the ability to create a vast maze full of treasure, traps, and monsters, but why would he? Let’s think about Nyarlathotep’s person-ality: he is the mind and voice of the Outer Gods, and what he primarily cares about is serving them. What if his goal in creating this dungeon is to keep up to date on how dan-gerous the most powerful adventurers in the world are? He doesn’t necessarily want to kill them—he just wants to know how powerful a threat they represent and to figure out how to challenge them. And if these top adventurers are weak enough, he can bring back the Old Ones to de-stroy the world with the flick of a metaphorical wrist.

Of course, the best way to ensure that he gets a good analysis of these adventurers is to tell them the unvar-nished truth. Let everyone know that there is wealth—as well as great danger—in the Twisted Pyramid to draw the finest adventurers available. Once the current crop of adventurers proves too craven and feckless to brave the pyramid, Nyarlathotep will know the world is ready for the end times. Thus, the players have two reasons to brave the pyramid: one obvious, one subtle. First, they can seek the wealth, which is genuinely there as a lure. And second, they might wish to save the world from the Old Ones’ return. (They may not know about this aspect of the adventure until they get to the pyramid, or perhaps only in retrospect.)

But how else could Nyarlathotep affect the dungeon crawl? Well, since he has a thousand forms, perhaps each separate dungeon level features its own avatar of Nyarla-thotep, starting out with comparatively weak forms, and working up to the most powerful. I would also suggest that each time the adventurers encounter Nyarlathotep, he speaks with them, mocking their efforts and making suggestions, foul offers, and promises.

This is a standard dungeon experience with a kick to it: the Mythos has added that little extra touch to bring it beyond the mundane. With this twist, you can turn Nyar-lathotep into an ongoing foil for the players and for your campaign, using a mere dungeon crawl as their introduc-tion to him.

using horror in an rPg environMenTMany of the creatures in the Mythos are so horrendously powerful that even a high-level group cannot kill them. Some of the entities described in this book are literally impossible to defeat. Don’t force such a confrontation upon your players without giving them warning. You don’t need much of a premonition—perhaps a shadow suddenly darkens the moon, or the city’s dogs suddenly cease their howling.

The entities of the Mythos almost always corrupt those who learn of them. Adventurers who investigate the an-cient lore of Yog-Sothoth or other Great Old Ones should do so through a sea of terrors and ethical or religious quandaries. Learning more about these entities should never become humdrum.

An adventure centered on the Mythos should be put

together in a style I call “layers of the onion.” The idea is that as the players uncover one layer of dark secrets, they expose another. This goes on and on: just as when you peel an onion, successive strata appear.

For instance, say the players are investigating an evil cult-worshiping nobleman or a haunted castle. But as they probe more deeply, you, the game master, can gradually show them the significance of this particular nobleman or the dark history of the site of the castle. As the players gather more information and penetrate deeper into the mysteries, this leads to other adventures.

In Lovecraft’s epic “At the Mountains of Madness,” the characters uncover some odd fossils, excellently preserved and reminiscent of the ancient tales of the Old Ones. The hero and his companion go scouting and find what seems to be a huge and complex rock formation inside a glacier. When they return to the camp, everyone has been killed, and the “fossils” are missing. The heroes are horrified and decide to follow the trail which leaves camp, headed toward the icebound rocks. This all occurs in the first layer of the onion.

They probe deep into the rocks and find tunnels under the ice which lead lower and lower. As they chase after the tracks of whoever (or whatever) killed their companions, they gradually come to realize that it is a true city, not just an unusual formation. Furthermore, non-humanoid entities, whose history is found in carvings on the walls, built the city millions of years ago. This is the second layer of the onion.

As the heroes penetrate deeper, and come upon more and more horrors, they realize that the “fossils” are actual living (albeit cryogenically-preserved) elder things. The heroes follow the path anyway, and the story culminates in an awful conclusion, where the heroes meet not the elder things preserved in the ice, but the dread things (shog-goths) that wiped out their species. This is the end of the story, but clearly it would be possible to extend it further.

For instance, a game master could have the heroes investigate the shoggoth “civilization” and find out that these amoeboid horrors are up to something (the fourth layer of the onion). Since shoggoths are not really mov-ers and shakers, no doubt something even worse than shoggoths is directing their efforts. And for what purpose? The destruction of all surface life? The return of the star spawn? The formation of a gigantic device designed to break the continent free from the world’s surface and form a new moon? Who knows? The wheels within wheels keep turning, and the players can continue following the tale forever.

Alternatively, they could progress a certain way down the stories, and then you, the game master, can switch to another storyline: a new civilization of nightmare crea-tures; an ancient tome with unspeakable secrets; some-thing else altogether. String together Mythos concepts and bury the heroes deep in the darkness.

The reason for this system of episodic revelation is because horror, by its nature, is difficult to maintain for a prolonged period of time. This is why horror movies typi-cally have only short moments of terror, interspersed with possibly ominous or tense sections in which non-horror-

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based scenes take place. In a similar way, horror novels are rarely as consistently terrifying as horror short stories.

Thus, each time a new layer of the onion is revealed to your players, there is an opportunity for a new shock, a new understanding. The players may wish time to discuss the ramifications (you may or may not allow this time, depending on the adventure’s needs), and certainly their understanding of what is going on will change.

You can also use this to up the ante. Let’s use another example: the town suffers from an outbreak of ghouls. The ghouls are a potent, intelligent foe. There are scary moments, desperate ambushes in dark alleyways, and so forth.

During the course of this conflict, the players uncover the second part of the storyline and learn that the ghouls are up to something–some grandiose plot. So now the player’s focus changes from physical danger to worrying about a larger threat–what are the ghouls up to? Instead of just defending the township, they now have to descend into the ghoul tunnels to find out the secret. Now the ghouls lay traps and call unholy allies to their aid. The ante has been raised for the players, not just in terms of danger, but in terms of what happens if they fail.

When the players finally discover what the ghouls are plotting, you the game master have the opportunity to transform the adventure once again in a third storyline, where you confront them with an existential threat! Per-haps the ghouls are replacing all the important humans in town with their evil changelings. Maybe the ghouls have accumulated enough sacrifices to summon and (they think) control a monstrous dhole to destroy the entire town. It’s even possible they plot to magically teleport the entire township to the Vale of Pnath, where they can feast at their leisure.

In this way, you have three simple, separate plot-lines, each with a different type of frightening threat, and you can keep up the horror ele-ment far longer and more effectively than in a one-shot adventure!

Turning an encounTer inTo an aDvenTureIt is perfectly plausible to plop down a gug guarding a treasure chest. The gug in this case would just be another monster—a bag of hit points hindering the players from gaining loot. A gug has some unique powers that you can use to your advantage in planning your encoun-ter. For example, gugs are completely silent, so players are likely unaware of the creature’s presence until it chooses to show itself. Since gugs have religious tendencies, perhaps it keeps an altar to its foul

deity in its chamber. Perhaps killing the gug triggers a curse which follows the party around.

With a little effort, the gug can be used for more. For example, gugs are an intelligent species known for crafting organized plans. Perhaps the gug was in that room for a reason? It’s not hard to extrapolate that after the party murders the gug for his loot, his fellow gugs might find the corpse, and—thirsting for vengeance— track down the par-ty. All of a sudden, perhaps when hotly engaged in another fight, a group of gugs emerges silently from the darkness and joins in the fight against the players. You’ve kept the adventure element of your game strong, but the gugs have taken on personality and perhaps even become a permanent part of your game. After all, even if the players manage to drive away or kill the pursuing party of gugs, this doesn’t mean they’re done with them: they might have to deal with gug hunting bands for the foreseeable future.

In the end, you have turned an almost random encoun-ter with a lone gug guarding some treasure into a recur-ring enemy that may plague the heroes’ future endeavors, potentially for an entire campaign, and woven in a Mythos thread that you can turn into something truly terrifying.

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7Mythos Player Character Races

Particularly notable among Lovecraft’s high fantasy stories is the novella The Dream-Quest of Unknown Kadath, from which stem the player races presented herein. Each has been chosen carefully for its interesting nature, useful-ness, and utility when set alongside the standard races of a fantasy campaign.

First the Dreamlands cats pad softly into view. All household or alley cats could potentially be Dreamlands cats: all that is required is the cats’ decision to return from their nightly trip to the Dreamlands while retaining human-level (though not human-centric) intelligence and purpose. Anonymity is their ally, for few humans expect stray cats to pose any threat.

Second in a Mythos game lurk the ghouls, which are emphatically not undead but rather undead-eaters. These entities might be degenerated humans, cursed by their grotesque behavior or other circumstances, or else “true” ghouls, born that way. Memories of their former lives—as well as the lives of others—play a prominent role in their savage society.

Next come the gnorri: amphibious entities with little un-derstanding of the surface world who nevertheless wish to participate in it. The gnorri are “blessed” with unusual and incredible abilities based on their astounding anatomy.

Finally, you’ll find the zoogs: well-known to readers of Lovecraft’s Dream-Quest, the zoogs are feral but diminu-tive horrors with secretive and enigmatic ways. Dangerous and unpredictable, zoogs are closely tied to the cosmic entities beyond.

After the four primary new player races, this chapter ends with brief introductions and player character rules for two more traditionally villainous human subtypes: the Leng folk and the Tcho-Tcho. These sorts of humans get more detail as enemies in Chapter 7 and Chapter 9.

We have enjoyed creating these races, testing them, and seeing them interact with the standard races. I think you will enjoy playing them as well.

—Sandy Petersen

The ghouls were in general respectful, even if one did attempt to pinch him while

several others eyed his leanness speculatively. Through patient gibbering he made

inquiries regarding his vanished friend, and found he had become a ghoul of some

prominence in abysses nearer the waking world. A greenish elderly ghoul offered

to conduct him to Pickman’s present habitation, so despite a natural loathing he

followed the creature into a capacious burrow and crawled after him for hours in the

blackness of rank mould.—H. P. Lovecraft, The Dream-Quest of Unknown Kadath

Chapter 2: Mythos Player Character Races

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