Open Mythos


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.


All 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.

Summary of Rituals

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

GM Resource: Designing New Rituals


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.

Summary of Artifacts

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

GM Resource: Designing New Artifacts


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).

Summary of Tomes

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.

Summary of Cults

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

Unnatural Entities

Summary of Entities

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:

  • POW statistic: this is important to mental conflicts between Protagonists and the alien horrors; other game stats which relate to physical attributes are not provided since the outcomes of physical challenges should be dictated by the needs of the story.
  • Common Types of Physical Attack: these are the ways in which the “god-like” power is most likely to inflict harm upon those it encounters; they are not exhaustive and are provided to allow a GM to quickly invent scenes where terrible carnage is meted out on those who have dared use force against such a titan.
  • Special Abilities: Unique powers that will shape any physical or mental encounter with the entity.
  • SAN Loss: the corrosive effect of witnessing the “god-like” entity in the flesh, or simply receiving its alien visions.
  • Quote: a source quote from the fiction of H.P. Lovecraft describing the entity or its influences.

The format for describing less powerful entities and races is more fully-featured in terms of game mechanics. It includes:

  • Full Game Statistics: STRength, CONstitution, DEXterity, INTelligence, and POWer are all listed on the same scale used for Protagonists (human normal ranges for each is 3-18).
  • Derived Characteristics: Hit Points (HP) and Willpower Points (WP).
  • Size Category: from smallest to largest — Extremely Small, Small, Medium, Large, Very Large, Extremely Large. Entities that are Extremely Small have an associated targeting penalty (making them harder to hit) while those that are Very Large or Extremely Large have a targeting bonus (making them easier to hit).
  • Movement: a description of the typical maximum distance the entity can traverse in a combat turn.
  • Armor: the number of Armor Points (if any) possessed by the entity.
  • vs Lethal Damage: describes how attacks that normally yield Lethal Damage against humans will affect this entity.
  • Attack Modes: for each mode, a % chance to hit is shown as well as the damage (either in terms of HPs or in terms of Lethality Rating). If an attack bypasses some points of target armor, this is also noted.
  • Skills: ratings for some of the entity’s skills, concentrating on those that may be important to a physical confrontation or efforts to evade.
  • Special Abilities: Unique powers (offensive, defensive, or other) that will shape encounters with the entity.
  • SAN Loss: the maddening effect of witnessing the entity in the flesh.
  • Quote: a source quote from the fiction of H.P. Lovecraft describing the entity or its influences.
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

GM Resource: Designing New Entities

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