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





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

Accelerated HealingHeal another person’s physical injuriesdays; 1d4 SAN2 turns; 1d4 WP, 1d6 SAN
Aklo SabaothMake contact with supernatural beingsweeks; 1d8 SAN1 hour; 1d8 WP, 1d10 SAN
AnnihilationTorture and kill through pure mind powermonths; 1d10 SAN1 turn; 1d8 WP, 1d10 SAN
Banish EntityBanish unnatural entitiesweeks; 1d6 SAN1 hour; WP approximately 2 × POW of the entity to be banished, 1d10 SAN
Body SwapTake control another person’s body, transferring your mind into itweeks; 1d6 SAN1 turn; 1d8 WP, 1d6 SAN
DHO HNA FormulaView or travel to distant placesmonths; 1d8 SANminutes; 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 WillTake over will of another person for a short perioddays; 1d4 SAN2 turns; 1d6 WP, 1d4 SAN
Elder SignProtection against unnatural forceshours; 1d6 SAN1 turn/1 hour; 10 WP per 10 m radius, 1d4 SAN
Elixir of LifeReanimate the recently deadweeks; 1d6 SAN5 minutes; 1d10 WP, 1d8 SAN
Erase MemoriesEliminate selected memoriesweeks; 1d6 SANhalf hour; WP = SAN of victim, 1d6 SAN
Essential SaltesRaise the dead from their physical remainsweeks; 1d6 SANminutes; 1d8 WP, 1d10 SAN
Forge Ancestral BondCreate a mystic bond with a future descendantweeks; 1d6 SANyears; 1d4 WP and 1d4 SAN per repetition of the ritual
Inflict HarmCause injury or illnessmonths; 1d8 SAN1 turn or minutes (depending on ritual variant); 1d6 WP, 1d10 SAN
Music of the SpheresAn invocation to Azathothdays; 1d4 SAN1 hour; 1d6 WP, 1d6 SAN + increase in unnatural knowledge by the same amount
Open Dimensional RiftAllows physical travel across vast expanses of dimensions, or through timemonths; 1d8 SAN1 turn; 1d8 WP, 1d6 SAN
Powder of Ibn-GhaziBriefly render invisible visible unnatural entities or objects visibledays; 1d4 SAN1 turn; 1d4 WP; 1 SAN
Prolong LifeProlong one’s life at the expense of others’ vitalityyears; 1d6 SANone hour; 1d10 WP, 1d6 SAN (animal sacrifice)/1d10 SAN (human sacrifice)
See Through The AgesView the future or past of a person, object, or placedays; 1d4 SAN1 hour; 1d4 WP, 1d4 SAN
Sign of KothWard against the passing of unnatural entitiesdays; 1d4 SANhours; 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 EntitiesSummon unnatural entitiesdays; 1d6 SANminutes to hours (approx. 2 to 3 × POW of entity in minutes); WP = POW of entity; 1d10 SAN
Voorish SignMagical symbol of protection and knowledgedays; 1d4 SAN1 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

ArtifactRitualsActivationSAN Loss
Cthulhu IdolAklo Sabaoth (Cthulhu), Call of Cthulhu (see Entity stats for Great Cthulhu)1D6 WP1D10 to use the Sabaoth
Golden Tiaras of the Deep OnesAklo Sabaoth (Dagon and Hydra), Summon Entities (Deep Ones).1D6 WP1D10
Great Race Mental Projection ApparatusOpen Dimensional Rift, Body Swap1D8 WP1D8
Jade Soul-AmuletSummon Entity (Hound of Death)1D4 WPNone
Mi-Go Brain CylinderNone1D4 WP0/1D4 to use, 1D4/1D8 to travel
Mi-Go Communication ImplantNone1D4 WP1/1D6
The Shining TrapezohedronDHO-HNA Formula, Summon Entity (Haunter of the Dark).1D4 WP or 1D10 WPUp to 1D6
The Silver KeyDHO-HNA Formula (Dreamlands)1D4 WPNone

GM Resource: Designing New Artifacts





Summary of Tomes

TomeLanguageStudy Time
Azathoth and other HorrorsTBDTBD
Book of AzathothTBDTBD
Book of DzyanTBDTBD
Brick Cylinders of KadatheronTBDTBD
Daemonolatreiae Libri IIITBDTBD
Ilarnek PapyriTBDTBD
The King in Yellow (play)TBDTBD
Liber Damnatus DamnationumTBDTBD
The Nameless BookTBDTBD
The NecronomiconTBDTBD
Pnakotic ManuscriptsTBDTBD
The Scientific reports of Dr. Herbert WestTBDTBD
The Seven Cryptical Books of HsanTBDTBD




Summary of Cults

Cannibal Cult of LengTBD
The Cthulhu CultTBD
Cult of the CrawlersTBD
Cult of the Wise OnesTBD
Esoteric Order of DagonTBD
Shepherds of Hastur (Cult of the Yellow Sign)TBD
Starry Wisdom SectTBD
Witches CovenTBD


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.
EntityDescriptionStatusSAN to Witness
AzathothLord of All Things, Blind Nuclear Chaos, Idiot GodOuter God1D10/1D100
Beings of IbFaithful Children of BokrugDreamlands Race1/1D6
BholesDestroyers of WorldsAlien Race1D8/1D20
BokrugThe CorruptorDreamlands God1D8/1D20
Cats of the DreamlandsGraceful and Mysterious Denizens of SlumberDreamlands Race0/1
Colour Out Of SpaceIncorporeal Devourer of VitalityAlien Race or Entity1/1D6 (Extremely Small or Small), 1/1D8 (Medium), 1D4/1D10 (Large), 1D6/1D10 (Very Large), 1D8/1D20 (Extremely Large)
Creeping CorpsesAnimated Corpse-Colonies of Squirming MaggotsProduct of Unnatural Rite1D8/1D20
Great CthulhuHigh Priest of the Great Old OnesGreat Old One1D10/1D100
Dagon and HydraFather and Mother of the Deep OnesPowerful Deep One “Gods”1D10/1D20
Elder ThingsAncient Creators of LifeAlien Race1D4/1D10
Formless HunterFlying Terrors and Hunting-HorrorsDimensional Horror1D4/1D10
GhastsMiddle Predators of the UnderworldDreamlands Race1/1D8
GhoulsImmortal Eater of CorpsesUnnatural Race1/1D6
GnorriGrand Architects of Underwater MarvelsDreamlands Race1/1D4
The God of the Sunken TempleNightmare Beneath the WavesGreat Old One?1D10/1D100
Great Race of YithInquisitive Librarians and Temporal MeddlersAlien/Temporal Race1D6/1D12
GugsCursed Titans of the Stygian DarknessDreamlands Race1D6/1D12
HasturPossible face of the King in Yellow???????
Hounds of DeathMerciless undead huntersUnnatural Race1/1D8
HypnosThe Lord of SleepGreat Old One1D10/1D20
Keziah MasonVicious Witch and Hideous NightmareImmortal Witch1/1D4
King in YellowMadness in Yellow TattersGreat Old One1D10/1D100
Leng FolkSemi-Human Merchants of CrueltyDreamlands Race1/1D6 (if undisguised)
Mi-GoThe Fungi from YuggothAlien Race1/1D8
Moon BeastsRuthless Slave Masters from the Dark Side of the MoonDreamlands Race1D4/1D10
Night-gauntsHorror of the nightDreamlands Race1/1D8
NodensLord of the Great AbyssGreat Old One1D10/1D20
NyarlathotepCrawling Chaos and Messenger of the Old GodsOuter God1D10/1D100
Polyp HorrorsInvisible and Semi-Substantial Masters of the WindsAlien Race1D6/1D12
Rat ThingsBrown Jenkins’ KinChangeling?1/1D4
Resurrected AbominationsFailed Attempts to Meddle With Life and DeathMistaken Creation1D4/1D10
Resurrected CorpsesThe Re-AnimatedOf Sorcery or Mad Science1/1D6
ShantaksMasters of the SkiesServitor Race1D4/1D10
ShoggothsFormless Horrors from Ancient EonsServitor Race (gone wild)1D8/1D20
Shub-NiggurathThe Black Goat of the Woods with a thousand youngGreat Old One1D10/1D100
Spiders From LengHunters on the desolate plains of LengDreamlands Race1/1D8
Star SpawnDreaming Servants of the Great Old OneAlien Race1D8/1D20
Winged ServantSpace-borne Eldritch Horrors from BeyondServitor Race? Alien Race?1/1D8
Yog-SothothThe Key and The GateOuter God1D10/1D100
ZoogsInquisitive Forest Dwellers of the DreamlandsDreamlands Race0/1

GM Resource: Designing New Entities

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