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The Open Cthulhu Mythos SRDClick to magnify

The Open Cthulhu Mythos SRD

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What primal, inconceivable source of age-old myth-cycles and haunting nightmares might I be on the brink of uncovering?


IMPORTANT NOTE: This PDF contains the text of a full set of game statistics describing the creatures, rituals, and artifacts from Lovecraft's original Cthulhu Mythos. In OGL terms it is a “System Reference Document” (or SRD). The statistics in this OGL are compatible with the Cthulhu Eternal, APOCTHULHU, and FHTAGN roleplaying games. While they give you everything that you’d need to incorporate the Mythos elements into a game they are not presented in a fully illustrated, typeset form as you would expect from a core RPG rulebook.

The Open Cthulhu Mythos is a compilation of game statistics for the original elements of (what became known as) H.P. Lovecraft's Cthulhu Mythos. They represent the most well-known elements of the cycle of myth invented by Lovecraft, but also elements which -- by virtue of original fiction copyrights having lapsed -- are now firmly in the public domain.

Meticulously researched by the German Lovecraft Society, these game stats were first published as the default game universe ("Spielwelt") for the German-language RPG FHTAGN. This edition translates them to English and sets them as resources which can seamlessly be used with any of the Cthulhu Eternal SRDs (see below) or with our best-selling APOCTHULHU RPG.

The SRD includes game descriptions of 40 Lovecraftian Entities (Gods & Monsters), 21 Unnatural Rituals described by Lovecraft, 8 Bizarre Artifacts, 14 Tomes holding terrible Mythos secrets, and 8 sinister Cults with Mythos associations. Here's the full list of elements included:

  • Entities: Azathoth, Beings of Ib, Bholes, Bokrug, Cats of the Dreamlands, Colour Out Of Space, Creeping Corpses, Great Cthulhu, Dagon and Hydra, Deep Ones, Elder Things, Formless Hunter, Ghasts, Ghouls, Gnorri, The God of the Sunken Temple, Great Race of Yith, Gugs, Hastur, Hounds of Death, Hypnos, Keziah Mason, King in Yellow, Leng Folk, Mi-Go, Moon Beasts, Night-gaunts, Nodens, Nyarlathotep, Polyp Horrors, Rat Things, Resurrected Abominations, Resurrected Corpses, Shantaks, Shoggoths, Shub-Niggurath, Spiders From Leng, Star Spawn, Winged Servant, Yog-Sothoth, Zoogs
  • Rituals: Accelerated Healing, Aklo Sabaoth, Annihilation, Banish Entity, Body Swap, DHO HNA Formula, Dominate Will, Elder Sign, Elixir of Life, Erase Memories, Essential Saltes, Forge Ancestral Bond, Inflict Harm, Music of the Spheres, Open Dimensional Rift, Powder of Ibn-Ghazi, Prolong Life, See Through The Ages, Sign of Koth, Summon Entities, Voorish Sign
  • Artifacts: Cthulhu Idol, Golden Tiaras of the Deep Ones, Great Race Mental Projection Apparatus, Jade Soul-Amulet, Mi-Go Brain Cylinder, Mi-Go Communication Implant, The Shining Trapezohedron, The Silver Key
  • Tomes: Azathoth and other Horrors, Book of Azathoth, Book of Dzyan, Brick Cylinders of Kadatheron, CTHULHU CULT (Angell’s Files), Daemonolatreiae Libri III, Ilarnek Papyri, The King in Yellow (play), Liber Damnatus Damnationum, The Nameless Book, The Necronomicon, Pnakotic Manuscripts, The Scientific Notes of Dr. Herbert West, The Seven Cryptical Books of Hsan
  • Cults: Cannibal Cult of Leng, The Cthulhu Cult, Cult of the Wise Ones, Cult of the Worm, Esoteric Order of Dagon, Shepherds of Hastur (Cult of the Yellow Sign), Starry Wisdom Sect, Witches Covens

All game content included in the SRD is fully open, allowing anybody to reuse the statistics and descriptions for any (commercial or non-commercial) purpose as long as it complies with the terms of the OGL 1.0a. This allows for virtually unlimited adaptation and copying of these game elements into scenarios, campaigns, and even brand new RPGs of your own devising.

If you want to partner them with one of our Open D100 Lovecraftian rulesets, the APOCTHULHU RPG provides options for Post-Apocalyptic play, but for current and historical eras our family of free/open Cthulhu Eternal SRDs currently support:

With more on the way. By pairing The Open Cthulhu Mythos SRD with one of these open D100 rulesets, you have hundreds of pages of rules and resources on which to build original creations, or adapt classic materials to run using a more modern and evolved version of the D100 rules.


We are releasing this SRD to support community creators who would like to produce their own original Lovecraftian RPG creations, but who need a  set of IP-free game resources to serve as a foundation to their own creative endeavors. As such, there are no real limitations on what you can do with this material (other than those described in the Open Game License).

Some examples of ways this SRD could be used:

  • Do you have some old Lovecraftian scenarios sitting around gathering dust for want of a free and open game system to use in their publication? Why not convert the scenario to work with Cthulhu Eternal rules and Open Cthulhu Mythos creatures and rituals? You can release them and direct readers to download the freely available SRDs to run them? Or even talk to us about bundling the SRD with the scenario PDF itself?
  • Do you have a fantastic idea for an innovative Lovecraftian game but the thought of having to re-create all the game stats for well-known Lovecraftian horrors is a distraction from your high concept? Well, you could always recycle some or all of the elements in this SRD to provide stats for your common adversaries or spell. Because the material is virtually 100% open content, you can copy/paste whatever rules you want into your original creation (as long as you release under the OGL and credit us as per the requirements of the license).

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Discussions (2)
Customer avatar
Matthew R April 26, 2023 5:37 am UTC
So what's in this document that isn't in the Cthulhu Eternal SRDs?
Customer avatar
Dean E April 26, 2023 6:08 am UTC
The Cthulhu Eternal SRDs are purely rules (character creation, skills, sanity, combat, etc). They contains zero game stats for Mythos creatures and such, just some guidelines to help GMs make their own.

This SRD on the other hand isn't a rulebook, but a description of the horrific entities, powers, artifacts, and groups which haunt a traditional Lovecraftian version of our world.

Thus, there is no overlap between the content in the Open Cthulhu Mythos SRD and the various CE SRDs. In fact if you paired the OCM with one of those, you'd have something close to the contents of an all-in-one Cthulhu Mythos RPG corebook (which traditionally cover both rules and "world" in the one volume).
Customer avatar
Matthew R April 27, 2023 6:56 am UTC
Thanks for the clarification!
Customer avatar
Cristian M April 24, 2023 1:48 pm UTC
This is great! Thanks for the fantastic work put into researching and re-releasing these as open gaming content.
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File Last Updated:
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This title was added to our catalog on April 23, 2023.