In his fiction, H.P. Lovecraft began to build a complex intermeshed web of weird-sounding extra-dimensional, alien, and otherwise weird beings. He also invented obscure tomes of forbidden lore and nefarious cults of misguided worshippers. He also encouraged fellow horror writers to borrow his strange creations and add them into their own stories; in return, Lovecraft baked some of his friends’ alien names into his later stories.
In the century since this vast game of collective myth-building began, the so called “Cthulhu Mythos” — a name coined long after Lovecraft’s death in 1937 — has grown to become a patchwork of creations that is both expansive and problematic from an Intellectual Property perspective. While there are undeniably some parts of this Mythos that are firmly in the Public Domain, other parts have been added by more recent writers (some still alive) who retain IP rights to their creations.
When building a cool game scenario or campaign, the last thing anyone wants to be thinking about is whether the inclusion of this or that alien name might trigger a nasty email from lawyers representing a fiction author or the estate of a dead author. To make things easier for creators, the German Lovecraft Society invested an enormous amount of time and effort to isolate the “open” parts of the Mythos — effectively the elements invented by Lovecraft himself for stories that have now fallen into the Public Domain. They also built game statistics for those creations.
If you’re looking for familiar Lovecraftian horrors to add to your game or scenario … and you DON’T want to get bogged down in the legalities of which author/estate to contact about which odd-sounding god, creature, or tome … these are your go-to Mythos elements. We have taken the work by our esteemed German colleagues and partnered with them to translate them to English and tweak the statistics so they work with our Cthulhu Eternal and APOCTHULHU RPGs.
The Open Mythos is divided into Rituals, Artifacts, Tomes, Cults, and Unnatural Entities.
USING THIS MATERIAL IN YOUR GAME OR PUBLICATIONAll content presented on this page is freely re-usable under an open license. All text is published under the Wizards of the Coast Open Game License (OGL) v1.0a. Click here for a copy of the full OGL license relating to this material. Everything on this page is considered “Open Game Content” under the terms of this license, and can be freely re-used in any publication that is similarly released under OGL v1.0a. No text is considered Product Identity, however the Cthulhu Eternal Logo is a trademark and thus not-reusable, except under a separate license (click here for information about our free compatibility logo license for Cthulhu Eternal) Original art assets (icons, drawings of Mythos creatures, etc) are all supplied under a Creative Commons (CC-BY) license, and can be freely re-used under the terms of that license. |
The descriptions of the following rituals are, for the most part, directly based on rituals described by Lovecraft himself. They should serve as inspiration and orientation for the Game Moderator to design his or her own rituals.
This format for ritual description is as follows:
Study: study duration; SAN loss.
Activation: duration; WP cost; SAN Loss.
Description: The summary of the effect, necessary actions and prerequisites of a ritual. Sometimes the successful performance of a ritual also requires certain skill values. Sometimes the effect causes an increase in unnatural knowledge.
| Ritual | Effect | Study | Activation |
| Accelerated Healing | Heal another person’s physical injuries | days; 1d4 SAN | 2 turns; 1d4 WP, 1d6 SAN |
| Aklo Sabaoth | Make contact with supernatural beings | weeks; 1d8 SAN | 1 hour; 1d8 WP, 1d10 SAN |
| Annihilation | Torture and kill through pure mind power | months; 1d10 SAN | 1 turn; 1d8 WP, 1d10 SAN |
| Banish Entity | Banish unnatural entities | weeks; 1d6 SAN | 1 hour; WP approximately 2 × POW of the entity to be banished, 1d10 SAN |
| Body Swap | Take control another person’s body, transferring your mind into it | weeks; 1d6 SAN | 1 turn; 1d8 WP, 1d6 SAN |
| DHO HNA Formula | View or travel to distant places | months; 1d8 SAN | minutes; variable WP depending on distance: 1d4 SAN (gaze, near) / 1d6 SAN (gaze, far) / 1d10 SAN (gaze, distant worlds); 1d4 SAN (gaze, earth) / 1d6 SAN (gaze to strange or mystical places) / 1d10 SAN (travel) |
| Dominate Will | Take over will of another person for a short period | days; 1d4 SAN | 2 turns; 1d6 WP, 1d4 SAN |
| Elder Sign | Protection against unnatural forces | hours; 1d6 SAN | 1 turn/1 hour; 10 WP per 10 m radius, 1d4 SAN |
| Elixir of Life | Reanimate the recently dead | weeks; 1d6 SAN | 5 minutes; 1d10 WP, 1d8 SAN |
| Erase Memories | Eliminate selected memories | weeks; 1d6 SAN | half hour; WP = SAN of victim, 1d6 SAN |
| Essential Saltes | Raise the dead from their physical remains | weeks; 1d6 SAN | minutes; 1d8 WP, 1d10 SAN |
| Forge Ancestral Bond | Create a mystic bond with a future descendant | weeks; 1d6 SAN | years; 1d4 WP and 1d4 SAN per repetition of the ritual |
| Inflict Harm | Cause injury or illness | months; 1d8 SAN | 1 turn or minutes (depending on ritual variant); 1d6 WP, 1d10 SAN |
| Music of the Spheres | An invocation to Azathoth | days; 1d4 SAN | 1 hour; 1d6 WP, 1d6 SAN + increase in unnatural knowledge by the same amount |
| Open Dimensional Rift | Allows physical travel across vast expanses of dimensions, or through time | months; 1d8 SAN | 1 turn; 1d8 WP, 1d6 SAN |
| Powder of Ibn-Ghazi | Briefly render invisible visible unnatural entities or objects visible | days; 1d4 SAN | 1 turn; 1d4 WP; 1 SAN |
| Prolong Life | Prolong one’s life at the expense of others’ vitality | years; 1d6 SAN | one hour; 1d10 WP, 1d6 SAN (animal sacrifice)/1d10 SAN (human sacrifice) |
| See Through The Ages | View the future or past of a person, object, or place | days; 1d4 SAN | 1 hour; 1d4 WP, 1d4 SAN |
| Sign of Koth | Ward against the passing of unnatural entities | days; 1d4 SAN | hours; 1D6 WP and 1D4 SAN against a specific type of being or 2D6 WP and 1D6 SAN if potent against all types of Mythos creatures |
| Summon Entities | Summon unnatural entities | days; 1d6 SAN | minutes to hours (approx. 2 to 3 × POW of entity in minutes); WP = POW of entity; 1d10 SAN |
| Voorish Sign | Magical symbol of protection and knowledge | days; 1d4 SAN | 1 turn; 1d4 WP, 1 SAN |
Tales of cosmic horror often feature Items with inexplicable powers, including the ability to open doorways or unlock unnatural knowledge. When such Artifacts fall into the hands of player characters, they provide evidence of things that should not exist, since their unique properties are utterly impossible to explain with known scientific principles.
This format for describing an Unnatural Artifact is as follows:
Rituals: which Unnatural Rituals (from those described elsewhere on the Open Mythos pages) may be cast by using the Artifact.
Activation Cost: WP cost to activate the Artifact.
SAN Loss: The mental damage created through the use of the artifact to tap the forces of the unnatural.
| Artifact | Rituals | Activation | SAN Loss |
| Cthulhu Idol | Aklo Sabaoth (Cthulhu), Call of Cthulhu (see Entity stats for Great Cthulhu) | 1D6 WP | 1D10 to use the Sabaoth |
| Golden Tiaras of the Deep Ones | Aklo Sabaoth (Dagon and Hydra), Summon Entities (Deep Ones). | 1D6 WP | 1D10 |
| Great Race Mental Projection Apparatus | Open Dimensional Rift, Body Swap | 1D8 WP | 1D8 |
| Jade Soul-Amulet | Summon Entity (Hound of Death) | 1D4 WP | None |
| Mi-Go Brain Cylinder | None | 1D4 WP | 0/1D4 to use, 1D4/1D8 to travel |
| Mi-Go Communication Implant | None | 1D4 WP | 1/1D6 |
| The Shining Trapezohedron | DHO-HNA Formula, Summon Entity (Haunter in the Dark). | 1D4 WP or 1D10 WP | Up to 1D6 |
| The Silver Key | DHO-HNA Formula (Dreamlands) | 1D4 WP | None |
Books that contain knowledge about the Unnatural knowledge are mostly old, extremely rare, very dangerous, and always unique. Just tracking down or getting hold of such a book should never be a trivial exercise. Studying such a tome painstakingly is the only way to gain benefits from its secrets, but such study will always have consequences for the reader. In addition to a loss of SAN from reading, some books have other special effects that apply when studying them. In particular, some tomes can affect the scholar to such a degree that it causes changes to the character’s motivations (e.g., making them fixate on something they learned).
| Tome | Language | Study Time & SAN Loss |
| Azathoth and other Horrors | English | Days; 1D6 SAN |
| Book of Azathoth | Unknown | Months; 1D10 SAN |
| Book of Dzyan | Senzar / English | Weeks/Days (translation); 1D10 SAN / 1D6 SAN (translation) |
| Brick Cylinders of Kadatheron | Language of the Dreamlands (only to be read in the Dreamlands) | Months; 1D4 SAN |
| CTHULHU CULT (Angell’s Files) | English | Days; 1D4 SAN |
| Daemonolatreiae Libri III | Latin | Weeks; 1D6 SAN |
| Ilarnek Papyri | Language of the Dreamlands (may only be read in the Dreamlands) | Weeks; 1D6 SAN |
| The King in Yellow (play) | English (or any other language) | Hours; 1D20 SAN |
| Liber Damnatus Damnationum | Latin | Weeks; 1D6 SAN |
| The Nameless Book | Latin | Weeks; 1D6 SAN |
| The Necronomicon | Arabic / Greek / Latin / English | (depending on the edition) Weeks (English) / Months (all others); 1D6 SAN (English) / 1D10 SAN (others) |
| Pnakotic Manuscripts | Latin / Greek / Language of the Dreamlands (depending on the edition) | Weeks / months (Dreamlands version); 1D4 SAN / 1D8 SAN (Dreamlands version) |
| The Scientific Notes of Dr. Herbert West | English | Days; 1D6 SAN |
| The Seven Cryptical Books of Hsan | Chinese / Language of Dreamlands (original version) | Days / weeks (original version); 1D4 / 1D8 SAN (original version) |
Knowledge of the Unnatural promises vast power, wealth and privilege. Thus it is not surprising that all around the world, groups of humans – cults – toil secretly in the worship of the Great Old Ones, hungry to share in their terrible power and wisdom. But not all cults are made up purely of misguided people willingly supplicating themselves before invisible gods – some coalesce around non-human creatures present on the earth, and some are groups where individuals become a member unwillingly.
| Cult | Description |
| Cannibal Cult of Leng | A society of undead ghouls and humans |
| The Cthulhu Cult | Worldwide worshippers of the Great Old One |
| Cult of the Wise Ones | Supporters of the Great Race of Yith |
| Cult of the Worm | Primordial Fertility Cult in Kingsport |
| Esoteric Order of Dagon | Hybrid Partners of the Deep Ones |
| Shepherds of Hastur (Cult of the Yellow Sign) | Opponents of the Mi-Go, followers of the Yellow Sign |
| Starry Wisdom Sect | Cosmic Knowledge in Exchange for Human Sacrifice – Worshippers of the Haunter in the Dark |
| Witches Covens | Keepers of ancient wisdom |
The descriptions of the following unnatural entities (races of creatures and unique beings) are, for the most part, directly based on horrors described by Lovecraft himself.
Two different formats are used to describe these entities — one for ultra-powerful “god-like” powers like Great Cthulhu or others of the Great Old Ones, and another for less powerful races of alien beings.
Entries for God-like powers described a minimum set of game parameters, since most encounters with such potent beings should be resolved in a narrative way rather than dictated by the whimsy of dice. To support a GM in weaving a compelling description of such a mind-blasting experience, a number of details are helpful:
The format for describing less powerful entities and races is more fully-featured in terms of game mechanics. It includes:
| Entity | Description | Status | SAN to Witness |
| Azathoth | Lord of All Things, Blind Nuclear Chaos, Idiot God | Outer God | 1D10/1D100 |
| Beings of Ib | Faithful Children of Bokrug | Dreamlands Race | 1/1D6 |
| Bholes | Destroyers of Worlds | Alien Race | 1D8/1D20 |
| Bokrug | The Corruptor | Dreamlands God | 1D8/1D20 |
| Cats of the Dreamlands | Graceful and Mysterious Denizens of Slumber | Dreamlands Race | 0/1 |
| Colour Out Of Space | Incorporeal Devourer of Vitality | Alien Race or Entity | 1/1D6 (Extremely Small or Small), 1/1D8 (Medium), 1D4/1D10 (Large), 1D6/1D10 (Very Large), 1D8/1D20 (Extremely Large) |
| Creeping Corpses | Animated Corpse-Colonies of Squirming Maggots | Product of Unnatural Rite | 1D8/1D20 |
| Great Cthulhu | High Priest of the Great Old Ones | Great Old One | 1D10/1D100 |
| Dagon and Hydra | Father and Mother of the Deep Ones | Powerful Deep One “Gods” | 1D10/1D20 |
| Deep Ones | Scourge of the Seas | Unnatural Race | 1/1D8 |
| Elder Things | Ancient Creators of Life | Alien Race | 1D4/1D10 |
| Formless Hunter | Flying Terrors and Hunting-Horrors | Dimensional Horror | 1D4/1D10 |
| Ghasts | Middle Predators of the Underworld | Dreamlands Race | 1/1D8 |
| Ghouls | Immortal Eater of Corpses | Unnatural Race | 1/1D6 |
| Gnorri | Grand Architects of Underwater Marvels | Dreamlands Race | 1/1D4 |
| The God of the Sunken Temple | Nightmare Beneath the Waves | Great Old One? | 1D10/1D100 |
| Great Race of Yith | Inquisitive Librarians and Temporal Meddlers | Alien/Temporal Race | 1D6/1D12 |
| Gugs | Cursed Titans of the Stygian Darkness | Dreamlands Race | 1D6/1D12 |
| Hastur | Possible face of the King in Yellow? | ??? | ??? |
| Hounds of Death | Merciless undead hunters | Unnatural Race | 1/1D8 |
| Hypnos | The Lord of Sleep | Great Old One | 1D10/1D20 |
| Keziah Mason | Vicious Witch and Hideous Nightmare | Immortal Witch | 1/1D4 |
| King in Yellow | Madness in Yellow Tatters | Great Old One | 1D10/1D100 |
| Leng Folk | Semi-Human Merchants of Cruelty | Dreamlands Race | 1/1D6 (if undisguised) |
| Mi-Go | The Fungi from Yuggoth | Alien Race | 1/1D8 |
| Moon Beasts | Ruthless Slave Masters from the Dark Side of the Moon | Dreamlands Race | 1D4/1D10 |
| Nameless City Reptilians | Those For Whom Death Died | Pre-Human Race | 1/1D4 or 1/1D6+2 |
| Night-gaunts | Horror of the night | Dreamlands Race | 1/1D8 |
| Nodens | Lord of the Great Abyss | Great Old One | 1D10/1D20 |
| Nyarlathotep | Crawling Chaos and Messenger of the Old Gods | Outer God | 1D10/1D100 |
| Polyp Horrors | Invisible and Semi-Substantial Masters of the Winds | Alien Race | 1D6/1D12 |
| Rat Things | Brown Jenkins’ Kin | Changeling? | 1/1D4 |
| Resurrected Abominations | Failed Attempts to Meddle With Life and Death | Mistaken Creation | 1D4/1D10 |
| Resurrected Corpses | The Re-Animated | Of Sorcery or Mad Science | 1/1D6 |
| Shantaks | Masters of the Skies | Servitor Race | 1D4/1D10 |
| Shoggoths | Formless Horrors from Ancient Eons | Servitor Race (gone wild) | 1D8/1D20 |
| Shub-Niggurath | The Black Goat of the Woods with a thousand young | Great Old One | 1D10/1D100 |
| Spiders From Leng | Hunters on the desolate plains of Leng | Dreamlands Race | 1/1D8 |
| Star Spawn | Dreaming Servants of the Great Old One | Alien Race | 1D8/1D20 |
| Winged Servant | Space-borne Eldritch Horrors from Beyond | Servitor Race? Alien Race? | 1/1D8 |
| Yog-Sothoth | The Key and The Gate | Outer God | 1D10/1D100 |
| Zoogs | Inquisitive Forest Dwellers of the Dreamlands | Dreamlands Race | 0/1 |
