This is a compendium of all those things squamous, rugose, and otherwise weird from the writings of H. P. Lovecraft and pals. Since most of these are eldritch monstrosities, a paragraph descriptor will be necessary for each. The stars are right.
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Notable Humans
Abdul Alhazred, AKA The Mad Arab
Author of the dreaded Necronomicon, and a Moslem apostate who worshiped the Great Old Ones. Described as an insane poet, Alhazred visited many strange and dark places filled with weird horrors. He was eaten by an invisible monster in broad daylight in 738 A.D. according to one record.
As Long as It Sounds Foreign: In Arabic, Abdul Alhazred makes no sense. Others have attempted to correct this, by saying that this is a corruption of the original name. Which is Truth in Television, since many ancient Arabic writers or works are better known by their bastardized names.
Author Avatar: Abdul Alhazred was Lovecraft's play name when he was younger.
Defictionalization: The Necronomicon listed in the Ohio University Library card catalog. L. Sprague de Camp, fantasy author and linguist, acted as Abdul Alhazred's "translator".
Death Faked for You: It turns out that Alhazred wasn't eaten, that being an illusion. Instead, he was kidnapped, tortured, had his tongue and eyes pulled out, and then killed.
Junkie Prophet: Considering the Mythos, Abdul does drugs to forget the horrors he has seen.
Shout Out: After Cthulhu and the Necronomicon, "The Mad Arab" is one of the most referenced elements in non-Mythos works.
Sincerest Form of Flattery: Many of Lovecraft's friends created their own unspeakable tomes in homage to Lovecraft's Necronomicon. Like Abdul, the fictional writers of these books meet dark ends.
Medical student, then a doctor. Postulating that human life was purely material, Herbert believed with the right chemicals could restart life. He and an assistant go about trying to prove this, conducting questionable experiments with... interesting results. Other than the setting of Arkham and Miskatonic University, West has little connection to the wider Cthulhu Mythos. He starred in a cult film trilogy in which he was played by Jeffrey Combs.
Mad Doctor: A graduate of the Miskatonic University Medical School no less.
Mad Scientist: Noble in intent, West's methods become increasingly unethical and deadly. It eventually drives him over the edge.
World War One: Herbert and his pal joined the Canadian military during the "Great War" as surgeons. For West, it's a great way to access more test subjects.
Randolph Carter
Early 20th century Boston author and occultist. One of the few recurring human characters within the Mythos, Carter is capable of entering the Dreamlands. Another Author Avatar: an unnoticed writer, prone to nervousness and depression. However, he is capable of courageous feats.
Seers: Since from a young age, Carter had the gift of prophecy, as well as a powerful dreamer.
The Quest: Several, including the well known Dream-Quest but also his travels beyond time and space.
White Anglo-Saxon Protestant: Standard for a Lovecraft hero. However, though he was raised as a Protestant Christian, Carter was materialistic later in life.
World War One: A veteran of the conflict, having served in the French Foreign Legion.
Outer Gods
Entities of the Mythos who operate on a cosmic scale, and tend to be far more powerful than most Great Old Ones. The Outer Gods are related to natural forces, such as Radiation, Time, or Childbearing. This classification originated in the Call Of Cthulhu RPG, and recently has been used within mythos literature.
Bigger Bads: As if the giant squid-headed horror and headless fat pervert wasn't bad enough, these guys far more powerful and dangerous.
Azathoth, AKA The Daemon Sultan
One of the two most powerful entities in the main canon (the other being Yog-Sothoth), Azathoth is a mindless, formless being of nigh-unlimited power that may have created the universe, which it dwells at the centre of with a coterie of (relatively) minor deities that serve as its "entertainment." Described as ultimate chaos. Lovecraft meant this deity to embody the mindless yet unbendable forces of physics.
"Before" and "After" Pictures: Done in Campbell's "The Insects from Shaggai", where the protagonist sees an image of Azathoth before he became insane. The Daemon Sultan once looked like a multi-legged clam, with cylinders for appendages, a mouthless face, and black hair. The narrator also sees the "After" picture...
Expy: Editor Robert Price thinks he's one for MANA-YOOD-SUSHAI from The Gods of Pegana, and indeed Lovecraft has mentioned in letters that he got ideas for his "Other Gods" (his term for what later became the Outer Gods) from that book. The Malleus Monstrorum sourcebook even makes MANA-YOOD-SUSHAI another of Azathoth's names.
The Ghost: At least in Lovecraft's stories, Azathoth was only referred to (though it is possible that he was intended to appear in the unfinished story of the same name). Some other writers have shown a bit more, but very few have actually had the nerve to have their protagonist come face-to-face with him.
Having A Gay Old Time: A more serious example, in which Lovecraft described Azathoth as The Nuclear Chaos. At the time, "nuclear" referred to something in the center, as in nucleus. As time went on, "Nuclear" became associated with atomic energy and weapons. Latter writers took advantage of this, and made Azathoth the patron of radiation.
Magical Flutist: The Servitors of the Outer Gods, who play flutes and drums to Azathoth. Needless to say, the music likely isn't pleasant to human ears.
Primordial Chaos: Lovecraft called it "Ultimate Chaos". Later authors made Azathoth an inversion: It wasn't always ultimate chaos. It became that way after losing its mind.
Summoning Artifact: The image of Daoloth is needed to contact him, as well as some sort of black plastic pentacle to hold him. You do NOT want to botch the pentacle part.
You Cannot Grasp the True Form: Daoloth's images are difficult enough for human eyes to perceive. Also, be careful when The Render reveals how reality itself really appears.
Ghroth, AKA The Harbinger
A red-brown planet sized Outer God that travels space. When he approaches a world, it awakens the local Great Old Ones which leads to a planet's demise.
The heart and soul of the Outer Gods, messenger of Azathoth. The most human of the Great Old Ones, as well as the most overtly malevolent. Has many "masks" - avatars that range in different shapes and forms. The most common visage is that of a tall, dark man with a regal appearance.
Ancient Egypt: Where it originally was worshiped (at least by humanity), gaining the suffix -hotep. However, The Mighty Messenger was so evil that Egyptians forbade its cult. The Black Pharaoh mask looks like the idealized king of this period, and maybe the one form that isn't outright frightening.
Deal with the Devil: He will try to sucker you into one if he simply doesn't try to gruesomely murder you. The latter is usually preferable unless you're the kind of person who doesn't mind what dealing with a malicious monster can lead to.
Evil Is Petty: Compared with Cthulhu's continent-destroying and Ghroth's world-shattering, Nyarlathotep is pretty petty in his schemes. This is likely intentional.
Fighting a Shadow: All of Nyarlathotep's physical forms are merely avatars. He is the personification of the soul of the Outer Gods, so whether he actually has a real body at all is not quite clear. Some of these Masks include:
Everything's Better with Samurai: Aku-Shin-Kage, a mask that plagues Japan. Looks like an armored samurai, but its face is covered in mouths. Can also take human form, which was Nobunaga Oda in the past, but usually a business man in the present.
Eye Beams: The Skinless One has a literal death glare – it can cause people’s skin to fall off.
Formulaic Magic: The Kruschtya Equation - a complex mathematical formula. Whoever solves it is possessed by Gnarly.
Hostile Weather: Yes, the "Crawling Chaos" evens manifests as weather, such as the Crawling Mist, Black Wind, and Messenger of the Old Ones.
Light Is Not Good: The White Man avatar, an angelic looking blond man with with white robes.
Our Banshees Are Louder: The Dweller in Darkness can create wind-like sounds (even when there is no wind) and strange cries at night.
Our Demons Are Different: The Black Demon and Dark Demon are traditional versions: black, furry, and snouted beasts. The Haunter of the Dark is a bat-like thing with a three-lobed eye.
Scary Black Man: How his Human avatars tend to appear. Although it should be noted that it's usually just the color of his skin (as in pitch-black) instead of overall physiognomy.
Weakened By The Light: The Haunter of the Dark could be instantly banished by light. But only to this avatar.
Gambit Roulette: Justified in this case it's perfectly reasonable to assume he can actually predict and engineer all possible outcomes.
Gender Bender: Has several female masks, including the Bloated Woman and the Queen In Red.
I Have Many Names: In addition to all its aspects, Gnarly has a number of titles: Crawling Chaos, Black Messenger of Karneter, Lord of the Desert, etc.
Mad Scientist: Lovecraft presents Nyarlathotep as this in the eponymous poem.
Name's the Same: In-universe example with the "Black Pharaoh", which could refer to the avatar or to the pharaoh Nephren-Ka. It could just be that Nephren-Ka was called that because of his evil acts, or taken up the title to enhance his power. Or, as some speculate, Nephren-Ka was really Nyarlathotep all along.
Nikola Tesla: The main influence for Nyarlathotep.
No, Mr. Bond, I Expect You to Dine: Has friendly conversation with Randolph Carter in The Dream-Quest of Unknown Kadath, though it's just to trick him.
One-Winged Angel: Destroy one avatar, and the Chaos transforms into something even more mind-shattering.
Only Sane Man: He is the living embodiment of the (rather malevolent) consciousness of the Outer Gods, and their messenger, and has taken special interest in mankind... this is not good for mankind.
Revision: L'rog'g (a twin-headed bat worshiped on Uranus) and Shugoran (The Black Man With a Horn) had no connection to Gnarly in the works they appeared in. Latter RPG material changed it so they became avatars.
Satan: A messenger (which is what the word "angel" means) for Azathoth who's shown to have resentment for the Outer Gods, one of few truly evil figures in the mythos, and a supreme manipulator. Yeah, Nyarly's the closest thing to the Devil, and possibly even more dangerous.
The Arkham witch coven believed that The Black Man was this. Whether or not this was intentional on Nyarlathoep's part or its what the witches just assumed is unknown.
Summoning Artifact: The Shining Trapezohedron, which calls the Haunter in the Dark aspect of Nyarlathotep.
Trickster Archetype: A very evil incarnation of it, especially in The Dream-Quest Of Unknown Kadath.
Unperson: The Egyptians took great lengths to remove any and all reference to Gnarly, though a few cults remain.
Shub-Niggurath, AKA The Black Goat of the Woods with a Thousand Young
Outer God of fertility. One of the most worshiped of the Mythos entities, she is revered by the Mi-go, K'nyani, and human cults past and present, among others. While never described directly in Lovecraft's tales, Shubby is often portrayed as a cloud with constantly changing hoofs and tendrils.
Affably Evil: Seemingly one of the least apathetic of the Outer Gods, a goddess of fertility who looks after her cultists. It's not as if anyone but her cultists would want her attention, however.
The Ageless: Can confer Biological Immortality to followers/sacrifices by ingesting them, and being reborn through her. The catch is, the person's body is horribly transformed into something unspeakable, which inspired (but not like) Fauns and Satyrs.
The Ghost: Lovecraft himself only referred to her and vaguely hinted at her character in his stories (most memorably The Whisperer In Darkness, where the Mi-Go were shown to worship her). It was through later writers that her true nature was revealed.
Hermaphrodite: Also has been called The Black Ram of The Forest With A Thousand Ewe, so Shub-Niggurath may have a male aspect as well. Then again, considering the Outer gods are beyond human comprehension, giving any "gender" to one would be problematic.
Mutagenic Goo: Some RPG materials have Shub-Niggurath producing a substance known as "Mother's Milk" that can cause radical biological changes in whoever ingests it.
The Smurfette Principle: Out of all Lovecraft's Old Ones, Shubby is the only one explicitly mentioned to be "female".
When Trees Attack: The Dark Young, which look like leafless trees with hooves. Its branches are actually tentacles.
Tulzscha
An obscure god, appears on Earth as pillar of green flame.
Playing with Fire: He's a pillar of flame, but with green color, very cold, and casting no shadow.
Retcon: In The Festival, his debut title, neither Tulzscha nor his servant monsters are named. Call Of Cthulhu RPG named him, and the monsters are stated to be Byakhee.
Yibb-Tstll
An obscure Mythos entity - a female, gigantic humanoid with detached eyes and clad in a great green cloak. Watching the universe revolve around it, she sees everything at the same time. Has great wisdom, only surpassed by Yog-Sothoth.
Alien Blood: The Black, Yibb-Tstll's ebon-hued ichor. Adding to the strangeness is that the blood is not fluid, but appears like snowflakes.
Bloody Murder: The Black can be used as by sorcerers to attack and destroy their enemies. It does involve a complicated ritual to do. Not to mention the spell could be reversed.
Covered in Gunge: Any victim of The Black is covered head to toe in the stuff.
Multiboobage: It has innumerable breasts, from which Nightgaunts feed upon.
The Omniscient: Knows a lot since she sees the universe revolve around her.
Tome of Eldritch Lore: The Cthäat Aquadingen, which hold details how to dream of Yibb, call The Black, or even summon the Ancient One! However, there's always some danger.
Yog-Sothoth, AKA The Key and the Gate
The other supreme deity of the original Lovecraftian canon, Yog-Sothoth is the living, sentient embodiment of the time-space continuum, although for reasons unknown he/it is trapped outside of our reality, only manifesting through various rituals. Is capable of impregnating human females. Its most well-known appearance is as a conglomeration of ever changing, glowing spheres, though this is just one of several forms.
Fartillery/Gasshole: Yog-Sothoth. "By a Stench ye shall know Him..." At the end of The Dunwich Horror, it lets out a shockwave of foul air so powerful it knocks trees over.
Light Is Not Good: Yog's avatar Aforgomon, who appears with a blinding flash, and only shows up when angered.
God of Good: Aforgomon is considered to be sacred to the folk of Hestan.
Ret Gone: Aforgomon does this to particular offenders such as those who screw up space and time by using Xexanoth's power. Instead of wiping them outright, the avatar speeds up the normal process of oblivion. Instead of years, people slowly forget the victim and any record eventually fades away in weeks.
Ancient, powerful horrors of the mythos, who are either sleeping or imprisoned. Often the center of cults, and encounters with them lead to death or worse. Originally, the term "Great Old Ones" included the "Outer Gods". Today, the term is used to describe mythos deities that are not dynamic or powerful enough to operate on a cosmic level.
Abhoth
One of the gods that live under Mount Voormithadreth in ancient Hyperborea. It's a pool of gray protean mass, which constantly spawns monsters from itself. No two of Abhoth's children are alike, some look like singular body parts, while others look like complex Mix-and-Match Critters. Abhoth grabs and devours most of its children, returning them to the mass, although some of them manage to escape.
Swallowed Whole: Well, without even single tooth, you don't have much choice.
Atlach-Nacha
A giant spider with a human face. Other forms include a young woman with multiple arms. He (or she) lives in a cavern under Mount Voormithadreth in ancient Hyperborea, and works on an endless task of bridging a chasm. Because of its appearance, Atlach is considered the regent of all spiders. The Spiders of Leng (huge purple spiders) are believed to be her children and servitors.
Odd Job Gods: Atlach-Nacha spends all her time bridging a vast chasm.
Byatis
A deity of divination and forgetfulness, Byatis is a massive toad-shaped being with a single eye, wings, crab claws, and a proboscis. Called “serpent-bearded”, its face is covered in tentacles. Originally called by the Deep Ones to Earth, it was trapped before Roman troops accidentally freed the being. By the 18th century, “The Berkeley Toad” came under the control of Sir Gilbert Morley, and used the creature to further his knowledge of the Mythos. It was kept in a cellar under a castle in Severnford.
Ascended Extra: Originally mentioned (very briefly) in Robert Bloch’s "The Shambler From the Stars". Ramsey Campbell then developed the character in his "The Room in the Castle".
Fat Bastard: What eventually happens to Byatis having feed so much on people, the toad grew so big that it couldn’t even leave its room!
Familiar: According to records, “The Berkeley Toad” was this to Sir Morley. Ironically enough, it's hinted that Morley ended up being eaten by his capative Old One.
Sealed Evil in a Can: At least twice. Once by the Elder Gods, and again when Sir Morley disappeared.
Chaugnar Faugn
A proboscidian Great Old One first mentioned in Lovecraft's "The Horror in the Museum" and later fleshed out by Frank Belknap Long. A grotesque being that pretends to be a statue of some nightmarish amalgamation of human, elephant and octopus, with a lamprey-like trunk, Chaugnar Faugn arrived on Earth eons ago from another dimension, at a time when only simple amphibians ruled the world. From these he shaped a servitor race called the Miri Nigri, which later interbred with early humanoids to form the Tcho-Tcho.
Continuity Snarl: As is common for the Mythos; supposedly, Chaugnar Faugn is the "grandfather" of the Tcho-Tcho, but there is never any mention of them worshipping him — instead, they are supposedly worshippers of Lloigor and Zhar.
Expy: In at least the D20 adaptation of Call Of Cthulhu, Chaugnar Faugn is depicted as looking like a monstrous rendition of Ganesha.
Gag Nose: He has a distorted elephant's trunk for a nose. Except it ends in a lamprey-like mouth and he uses it to feed on blood.
Lightning Bruiser: He looks like a fat human/elephant hybrid. When he wants to, though, he can move incredibly fast.
Silicon-Based Life: Chaugnar Faugn appears to be a statue made from some unidentifiable mineral. However, he's still alive and active... when he wants to be.
Cthulhu
The monstrous high priest of the Great Old Ones, sleeping in the sunken city of R'lyeh until 'the stars are right' and he can awaken his kin to resume their rule of Earth. A gigantic humanoid form with a squid-like head and dragon wings.
Cthulhu's genealogy was detailed by Lovecraft in one of his many letters. Cthulhu is the son(?) of Nub, one of the Twin Blasphemies. In turn, Nub and Yeb (the other twin) were spawned by Shub-Niggurath and Yog-Sothoth.
Clark Ashton Smith has makes Cthulhu and Hzioulquoignmzhah cousins, having shared the same ancestor named Cxaxukluth.
Badass Family: His kids with Idh-yaa are incredibly dangerous and powerful.
Do Not Taunt Cthulhu: Happens in "The House of Cthulhu", in which a band of barbarians go to R'lyeh. The leader believes Cthulhu is nothing more than a myth to scare away the weak, and his "tomb" holds vast riches. Let's just say he's wrong.
Mini Mook: His servitors The Star-spawn of Cthulhu, who are basically smaller versions of Big C. Even then, they're still very large relative to a human.
Ramming Always Works: Gets rammed into by the motor boat of the one person who survives him, breaking him up and forcing him back into R'lyeh, which promptly sinks.
Signs of the End Times: Every time R'lyeh begins to rise to the surface, strange events occur around the planet: people have dark nightmares, hysteria rises, and cult activities increase.
Telepathy: If not blocked by water Cthulhu can send out dreams to communicate with Cultists, and cause nightmares for anyone sensitive enough.
Elemental Embodiment: Derleth created an Elemental Theory, in which certain Great Old Ones were classified by the four classical elements. However, Derleth ran into a problem: no Great Old One could be considered a Fire Elemental. So Cthugha was created to fill in the gap.
The Swarm: Fire Vampires tend to appear in large numbers, especially when accompanying the Burning One when it is summoned.
Cthylla
The secret daughter of Cthulhu, and described as a huge, red octopus with six eyes and wings.
Crazy-Prepared: Cthylla serves as a backup plan. Should Cthulhu be ever truly destroyed, the Great Old One is reborn in his daughter's womb.
Dark Secret: Cthulhu does not want anyone to know Cthylla exists. And the few humans that discover the Cthylla's purpose go mad.
Daddy's Little Villain: Wither or not by choice, being Cthulhu's daughter alone makes her an enemy of mankind.
Knight Templar Parent: Played with, Cthulhu goes great lengths to protect his seed, but not because he cares for Cthylla. Any human emotion is beyond the Great Old Ones.
Moe Anthropomorphism: Notable since it's easier searching for art depicting Cthylla as human girl than octopus.
Eihort
A giant gelatinous oval with many legs, Eihort wanders the labyrinth-like underground tunnels of the Severn Valley. When encountering a mortal, Eihort will chase and corner them, then offer to lead them out of the tunnels in return for letting it implant its egg inside their body. Should they refuse, Eihort will just smash them into a bloody pulp...which isn't really worse than those who accept its offer, as the egg will eventually hatch, and the victim's body will shatter into countless brood of Eihort.
Body Surf: The upside to Eihort's bargain: It'll let you experience other lives in other places. Of course, the reverse is true: Eihort's servants could jump into the Bargainer's body, and have that person face some rather horrible experiences.
First born of Cthulhu, this Great Old One visage is so horrific that merely glimpsing it leads to... something unspeakable. Once ruling prehistoric Mu where its cult dominated, served by the Lloigor.
Ascended Extra: Considering the similarities, Ghatanothoa might have been just another name of Cthulhu back when Lovecraft introduced him.
Once trapped inside a meteor, Glaaki now resides in the lake created by impact of said meteor in the Severn Valley. Looks like a giant slug with a mouth, eye-tip tentacles and lots of metallic spines. When Glaaki stabs people with its spines, it injects fluids that turn the victims into zombies which it can controls using psychic power.
Our Zombies Are Different: After a few decades, Glaaki's zombies becomes sensitive to sunlight. If exposed, they suffer from "The Green Decay".
Recurring Dreams: People who live by Glaaki's lake have some terrible nightmares. Except it turns out it's a Flashback Nightmare, and Glaaki is sending them out to dreamers.
"Half-brother" of Cthulhu. Doesn't mean they get along with each other. Known to be the patron of decadence, nihilism, and shepherds. Also the mate of Shub-Niggurath, and possibly fathered some of her Thousand Young. His most well known avatar is the King In Yellow (a tall masked man-thing wearing yellow rags). Other depictions includes that of a octopoid, but Hastur's true form is unknown.
Ascended Extra: When Lovecraft added Hastur to mythos, all he did was just mention it among a list of eldritch names without any elaboration. Derleth made Hastur into a Great Old One, since Ambrose Bierce originally had it as a deity.
Bright Is Not Good: If he takes a humanoid guise, it will often be brightly clothed. He's not any less dangerous.
Body Horror: Whoever makes the Unspeakable Oath ends up dying and becoming possessed by Hastur. Their body becomes scalier, grotesquely obese, and their limbs seem boneless.
Composite Character: Hastur is essentially a mash-up of several interpretations from several different sources, each either borrowing or name dropping the previous source. John Tynes finally combined the various aspects, especially the themes of from the original The King in Yellow, for the Call Of Cthulhu RPG.
Light Is Not Good: In addition to his yellow robes, Hastur sometimes appears with a halo. He is also usually depicted with angelicwings for no discernible reason.
Tsathoggua's "cousin" living in the upper atmosphere of Saturn, where he fled to avoid irritating worshipers and cannibalistic family members. Similar in appearance to Tsathoggua, but with a long neck and many small, elephantine feet.
Affably Evil: Possibly the most harmless of Lovecraftian deities, simply by wanting to be left alone.
Great Old One that is humanoid in appearance, with glowing red eyes. Limited to frozen wastes, Ithaqua can literally walk on wind as if it was solid ground.
Alien Abduction: Tends to kidnap people, typically sacrifices, and even entire towns if need be.
Elemental Embodiment: Like Cthugha, Ithaqua was introduced into the mythos to balance out the Elemental Theory. In this case, The Wind-Walker is an Air Elemental.
Grim Up North: This Old One tends to haunt Alaska and Siberia.
Leave No Witnesses: Anyone who sees Ithaqua is bound to be hunted down by him.
Mars Needs Women: Ithaqua attempts to reproduce with humans, apparently so his children would have his powers, but not be imprisoned by the Elder Gods.
Not Quite Flight: They don't call him the The Wind-walker for nothing.
Originally from Yuggoth, Rhan-Tegoth came to Earth millions of years ago, settling in what would become the arctic. However, Rhan went into hibernation and can't move without some outside aid. One of the more unfortunate Old Ones, as he got stuck being used as some statue in a museum. Physically, he's very tall, covered in small tentacles, has six serpentine appendages with black crab pincers, a three-eyed and gilled head, a globular torso, as well as a proboscis.
Human Sacrifice: Played with, the blood of any living thing is sufficent to awake Rhan.
Gods Need Prayer Badly: Apparently went into hibernation after his original followers abandoned him. Although, it's more due to that Rhan-Tegoth needs blood to sustain himself than prayer.
Refuge in Audacity: What do you do with a monster that's been sleeping for eons? Stick him in a wax work display!
Wax Museum Morgue: The guy who found Rhan-Tegoth runs one of these. Subverted in that some of the statues were various horrors of the Mythos, instead of people.
Shudde-M'ell
Leader of the Cthonians: worm-like monsters with a squid-like head. Shudde appears like a larger form of a Cthonian, and possibly the progenitor of the species.
Broke Your Arm Punching Out Cthulhu: While the Wilmarth Foundation managed to wipe out many Cthonians, they lost a lot of people and resources. Also occurred when they tried nuking Shudde-M'ell himself, and failed.
Nigh Invulnerability: Shuffle-M'ell can take on a nuclear explosion and live, as well as able to bore through Earth's crust and survive in the planet's mantle.
Made of Iron: Cthonians are able to resist great pressures and temperatures.
Mama Bear / Papa Wolf: Generally, it’s a bad idea to mess around with Cthonian eggs.
Mental Fusion: Groups of Cthonians can combine their psychic powers to overcome any protection.
Psychic Link: All Cthonians are linked to each other, allowing to know exactly what other one knows.
Sandworm: Cthonian physical appearance suggests this, but they're more like the Horta from Star Trek. They can easily burrow through rocks, and can resist high pressure and heat. Although, the Cthonians and Sandworms do share the same...
Weaksauce Weakness: Cthonians don't take well to exposure to, of all things, water. Which helps explain why they usually tend to stay safely miles underground rather than visit Earth's mostly water-covered surface, of course.
Telepathy: The worms can influence a person's thoughts and emotions, causing them to make mistakes or force them to stay in one location.
Tome of Eldritch Lore: The G'harne Fragments, which tell of the history of the titular Cthonian city.
Old One whose visage is that of a furry, huge toad. The Sleeper was born outside the solar system, where he immigrated with his family to Yuggoth, and eventually making his way to Earth. He briefly resided under Mount Voormithadreth, and is often mentioned in the Hyperborean Cycle. Tsathoggua currently resides in N'kai, deep under the Earth under red-lit Yoth. He is served by the Formless Spawn, black ooze capable of changing shape.
Oh Crap: Was once a popular deity among the K’n-yani. When they discovered N'kai and some horrid things down there, they quickly removed any imagery or worship of the toad.
Portal Door: The titular The Door to Saturn was given by the Toad as a gift.
The Parchments of Pnom, which chronicles the genealogy of Tsathoggua and several Great Old Ones. Unlike some other examples, it's not notably dangerous.
The Book of Eibon (aka the Liber Ivonis), which told of the adventures of the titular Hyperborean wizard. Ebion also recorded Tsathoggua's secrets and rituals in the book.
Yig
The half-human Father of Serpents, this Old One is the patron of snakes. May have been the inspiration for the Aztec Quetzalcoatl, Yig was worshiped in North America by Plains tribes and the K'n-yani. Very impulsive and tyrannical, but beneficial to those kind to his "children".
The second son of Cthulhu, resembling a really large humanoid frog with a single eye. Imprisoned in the Abyss of Yhe by the Elder gods. In ancient Mu, he had a cult led Zanthu. Served by the Yuggs, giant things resembling white flatworms.
That's No Moon: When Zanthu attempts to free Ythogtha, he mistakes the creature's fingertips as mountains.
Tome of Eldritch Lore: The Zanthu Tablets, inscribed by the titular wizard on black jade. It tells of his struggle with Ghatanothoa's cult, as well as the failed attempt to release Ythogtha.
Y'golonacoh gods, you've doomed us all!
Trapped behind some wall somewhere, the Defiler is the Old One of Squick. His earthly manifestation is that of a fat, headless body with mouths on its hands. Typically seeks out closet perverts, offering them to become his servants in exchange to experience their sick desires.
Brown Note: Merely reading his name in the right context is enough to summon him.
DepravedOmnisexual: Implied, although this may be a way of satisfying the needs of his respective hosts.
The Unfettered: He will, quite literally, do anything to escape his prison.
Zhar and Lloigor, AKA The Twin Obscenities
Originally from Arcturus, these two horrors now inhabit the Plateau of Sung, in the underground city of Alaozar. Both appear to be extremely large masses of tentacles, of which Lloigor has wings. Both are served by the Brotherhood of the Star Threader, a cult of Tcho-tcho.
Entities of the Mythos who oppose the Outer Gods and the Great Old Ones. While helpful to humanity, they're still just as prone to Blue and Orange Morality, at least in theory.
Bast
Based of the mythological goddess of the same name, Bast is the Elder God of Cats. Was classified as Elder God in the Call Of Cthulhu, since Lovecraft was rather fond of felines. Bast was also used in several Mythos tales by Robert Bloch. The story of The Cats of Ulthar is also ties to her in the Call Of Cthulhu. For further details, check out the Egyptian Mythology Character sheet.
Hypnos
Another deity appropriated from Mythology, this time from Greece. Listed as an Elder God of sleep in Call Of Cthulhu, and as such Lord of Dreams. Other than that, little is known of this being.
Calling Card: Apparently leaves behind statues of himself.
The Ghost: In Lovecraft's short tale "Hypnos", the character's friend fears something that the narrator or reader never sees. In fact, Hypnos is almost never depicted in any artwork, except only as a marble bust.
Pillar of Light: If for some unknowable reason a dreamer attracts his attention, Hypnos will seek that person out, and pull them up in a golden light.
Kthanid
Brother of Cthulhu. Visual appearance is like that of Cthulhu, but only with golden, peaceful eyes. A controversial subject in the Mythos, as he's clearly depicted as being good in a universe filled with alien, amoral beings.
It's Personal: Bears a special grudge against the Great Old Ones, since they killed his mate and offspring.
Palette Swap: Except for the eyes, there's no physical difference between Kthanid or Cthulhu.
Nodens, AKA The Lord of the Abyss
Named after an obscure Celtic deity, Nodens is unusual in that his main apparition is an old man. Apprently a great hunter, seeking out the servants of the Great Old Ones. Typically seen riding in a seashell chariot drawn by fantastic beasts. Opposes Nyarlathotep.
Anti-Villain: Described as almost friendly to the humans he speaks with. He also apparently has a strong dislike for Nyarlathotep.
Egomaniac Hunter: He hunts the servants of Nyarlathotep and other horrors. But not because Nodens cares for humanity, but because the Great Old Ones provide the best sport.
Lesser known Elder God who appears in the writings of Henry Kuttner. Sometimes appears as a cloaked, hooded being, enveloped in green flames, with fiery eyes. He may otherwise appear as a misty, silvery being with an inhuman face.
Alien Geometries: Vorvadoss' body seems to follow an alien pattern.
Dissonant Serenity: As alien and disconcerting Vorvadoss may appear, people around the Kindler of Flame feel a wave of assurance in its presence.
The "chief cosmic power" hostile towards time, known on the world of four suns named Hestan. Not considered an Elder God properly, its nature makes it opposed to at least one Outer God.
Arch-Enemy: To Aforgomon, lord "of the minutes and the cycles" and avatar of Yog-Sothoth.
Gods Of Evil: To the priests of Aforgomon since its effects on time causes the logical cycles of nature to go slightly out of whack.
Time Master: As the bane of sequential time, the Lurking Chaos can cause people and entire planets to relive a moment in their past.
This Is Unforgivable: Using its power is considered too blasphemous, even for evil sorcerers. As one in The Chain of Aforgomon points out:
"Gladly would I help you... animate her still unwithered body and draw it forth from the tomb. But that which you purpose is another matter. You alone must perform the ordained rites, must speak the necessary words: for the consequences of this thing will be direr than you deem."
Other Creatures
Various monsters and aliens. Some act as servants of the Great Old Ones, while others are relatively independent.
Byakhee
Beings that live in interstellar space, noted for their "great wings". Capable of traveling interstellar distances, they can be summoned to be used as transports. Just remember to take some Space Mead or a space suit, since you still need some sort of protection against the cold vacuum. Servitors of Hastur.
Speak of the Devil: Mentioned in the 1980 Dungeons & Dragons Deities and Demigods Cyclopedia, that Hastur sends Byakhee to kill whoever speaks his name.
Colour Out of Space
Creature from outer space, whose visible manifestation is a unknown hue. Contact with earthly life leads to ... terrible fates.
Fictional Color: When heated in a spectroscope, a meteorite that carried the Colour "displayed shining bands unlike any known colours of the normal spectrum". A globule inside the meteorite and vegetation grown in the area where the meteor fell also display the non-spectrum colors. The Colour monster itself is made up of these colors.
Fisher Kingdom: The Blasted Heath, which was once a farm before everything began to mutate and turn into grey dust.
Underwater Ruins: The Blasted Heath, once the Arkham reservoir is built. Unfortunately, the plant life around the new water source has become rather twisted.
Cthonians
See Great Old Ones: Shudde-M'ell
Dagon/Deep Ones
A giant, ocean-dwelling being. One of the less actively malicious beasties - apparently wants some peace and quiet more than bringing the world to an end. Not that that's going to help you if you accidentally enter his domain, though. Progenitor of the Deep Ones, a similarly isolationist underwater civilization of fish-people with a certain... interest in humanity. Physically, Deep Ones are humanoid, a cross of fish and frog, with grey-green skin, white bellies, webbed paws, and gilled necks.
Body Horror: The below-mentioned hybrids start out seemingly human. And then, after a few years, they start to mutate...
Cult: The Esoteric Order of Dagon in Innsmouth, which the humans collaborators of the Deep Ones use in worship and controlling the town.
Aliens that once colonized Earth billions of years ago. They developed a highly advanced civilization, and they accidentally lead to life arising on Earth in the process of creating the shoggoths. They're described as a barrel-shaped body with a starfish-like head and feet. Featuring radial symmetry, they have five eyes, tentacles, wings, feeding tubes, and brain lobes.
Batman Can Breathe in Space: Subverted, the Elder Things could travel through deep space, but only by absorbing "certain chemicals". They end up losing this knowledge, and end up trapped on Earth.
Bizarre Alien Biology: At one point Dyer states that the aspects of their biology that make them so long-lived and resilient are probably beyond human understanding.
Creating Life Is Unforeseen: Hinted that terrestial life could be the unexpected consquence of the Elder Ones trying to grow food and Shoggoths.
Disintegrator Ray: Used "curious weapons of molecular and atomic disturbances".
Heroic Neutral: Long gone, for the most part, by modern times, but their enemies coincided with many of those that now trouble humanity. The narrators of the story in which they appear even compare them to human beings.
They're also the only inhuman race Lovecraft portrayed with any kind of sympathy, explaining the frenzied murder of the researchers in At The Mountains of Madness as a hysterical reaction to unknown circumstances. Imagine waking up after sleeping for thousands of years and finding one of your kin dissected on a table.
Made of Iron: Capable of living under deep sea pressures.
Solar Sail: As a result of advances in science, later writers explained that the Elder Things used their wings as living solar sails.
Starfish Aliens: Literally in this case, with the Elder Thing's radial physiology and starfish-shaped heads, though they are some of the more comprehensible aliens in the mythos.
Unreliable Expositor: While studying their historical art, Dyer considers the possibility that the Old One’s history may be colored by their pride. The professor wonders if the alien matter of the Star-Spawn and Mi-go are mere mythological constructs to explain the Elder Thing’s defeats. It is also notable that their annals don’t mention the Yithians either.
Vestigial Empire: After Shoggoth rebellions, wars against Cthulhu's spawn, the Great Race, and the Mi-go, and the cooling of Earth, the Elder Things are reduced to this.
Fthaggua
Described as a sphere of blue-flame, Fthaggua is similar to Cthugha. However, where as Cthugha is imprisoned, Fthaggua is free and riding across the universe on the comet Ktynga. He is served by his Fire Vampires, which appear as red lighting. It's unknown if Fthaggua is a Great Old One or not, also if it has any relation to Cthugha.
Hive Mind: Fthaggua and his Fire Vampires are described as such.
Our Vampires Are Different: A radical example, although the basic synopsis is the same. Upon destroying a victim (akin to spontaneous combustion), the Fire Vampires absorbs both the lifeform's energy and memories.
Weak gods of the Earth who reign over Earth's Dream Land. Not even remotely powerful as the other Ancient Ones, although they are still worshiped in the Dreamlands. They appear to be similar to humanity, and distinguished by certain facial features. For whatever reason, the Great Ones are protected by the Other Gods, which include Nyarlathotep. Not to be confused with the Great Old Ones.
Deface of the Moon: Carved on the hidden side of Mt. Ngranek is a portrait of the Great Ones. It proves to be an important plot point in The Dream-Quest Of Unknown Kadath.
I Just Want to Be Normal: Maybe. In The Dream-Quest of Unknown Kadath, Nyarlathotep tells Randolph Carter how the Great Ones desire to abandon their godhood and live as normal humans in the waking world.
Interspecies Romance: The younger Great Ones tend to go down to Earth in disguise and take human women as wives.
Physical God: Rather limited ones at that, capable of being tricked by a mortal who is wise enough.
Great Race Of Yith
A highly intelligent race that lived on Earth long before humans. Their bodies consist of fleshy cones with four tendrils (two ended in pincers, one a mouth and one a pair of eyes) sticking out of the top. They ruled a portion of the Earth that includes what is now Australia when Cthulhu was active. They use psychic powers to leap from body to body across time. Their society is described as socialist and placing a high value on individual intelligence. The Great Race of Yith is wiped out in a war with the Flying Polyps, but will be re-created in the future thanks to their time-traveling powers. Yithians come across as the closest thing to a "good" race out of the original Lovecraft critters.
Badass Bookworm: one of the more (conventionally) intelligent races in the setting, and the Mi-Go and the Star Spawn of Cthulhu respected them.
Bizarre Alien Biology: not unexpected considering the setting. They also reproduce by spores....
Grand Theft Me: Usually combined with the mental time travel mentioned below. Can be temporary for research purposes or permanent.
Inferred Holocaust: The bodies most commonly associated with them? Those belonged to beings native to Earth before the Yithians used their mind-swapping powers to leave their own dying world for ours...
Laser-Guided Amnesia: Before reversing a temporary body swap, the 'guest' mind is stripped of its memories of its stay with the Yithians. As Professor Peaslee (of "The Shadow Out Of Time" fame) will attest, the process isn't always quite 100% effective.
Shock and Awe: The main weapon of the Yithian armies is a lighting-shooting device that looks like an old camera.
Time Travel: Of the mental variety, and the source of the appellation "Great Race," as they were the only species to master it.
Ghouls
Cannibal humanoids with rubbery skin, bony claws, and dog-like faces. They tend to live underground, lurking near graveyards.
Changeling Tale: Ghouls are also known for kidnapping babies and replacing them with ghoul babies. Don't worry though, they just teach the abducted children how to become ghouls.
I'm a Humanitarian: Played with, the Ghouls are known for eating corpses. Although sometimes, they do attack people.
Good All Along: Although presented as horrific, they are sometimes presented in a positive light, being loyal and helpful to some. Considering the Mythos being filled with unspeakable, apathic horrors, Ghouls are one of the nicer species one can encounter. If one knows their language...
Grave Robbing: The Ghouls probably call this "Grocery Shopping".
Was Once a Man: Hanging out with Ghouls long enough can transform a human into one.
Gugs
The subterranean giants of Dreamlands. Gugs have vertical mouth, ran from the top to the bottom of the head, and each arm split at elbow into two forearms. Said to be banished to the Underworld by the Great Ones.
To Serve Man: And since humans are rarely encountered in Dreamlands's Underworld, we're kind of legendary delicious.
Hounds of Tindalos
Creatures from the primordial past that are capable of traveling through time. They are only able to enter our dimension through angles.
And Man Grew Proud: Due to some unspeakable act in near the primordial past, the Hounds became “foul” while normal life remained “pure”. The event itself was forgotten, but the myths such as The Fall from Genesis are allusions to this event.
The Ghost: The Hounds are never seen in the original story they debuted. They're only described as "hungry" and "foul" by one of the characters.
Hellhound: Described as this, but more for their ravenous, relentlessness hunger than for their physical appearance.
Immortality: Theoretically they have Biological Immortality, since no enzymes exist within the bodies of the Hounds.
The Juggernaut: Once they catch the scent of someone, they will keep on hunting until they get their target.
Insects from Shaggai, AKA Shan
Extraterrestrials that worshiped Azathoth. Although highly advanced, this species was also extremely decadent. The Shan are about the size of a pigeon, with leathery wings, large lidless eyes, ten legs with tentacles, six brain lobes, and three mouths.
Asshole Victim: Their homeworld was destroyed when a celestial body (likely Ghroth) passed. Considering their extreme decadence, the Shan deserved it.
Futuristic Pyramid: The Insects' conical-shaped temples to Azathoth, which are not only capable of teleportation, but also have gateways that allow direct contact with "The Demon Sultan".
Intangible Man: Because of their affiliation with Azathoth, the Insects are able to phase through organic matter.
Mass Teleportation : The Shan are well versed in teleportation technology, capable of transporting their temples across interstellar spaces.
Oh Crap: Twice, often after discovering something disturbing on a planet they visited. And most likely the third time when they realize that Earth's atmosphere interfere with their temple's teleportation system.
Puppeteer Parasite: With their phasing abilities, and in combination with their psychic powers, the Shan are able to infest and dominate humans.
Slave Race: The Xiclotl, tall, meat-eating creatures, which the Shan conquered.
When Trees Attack: To humans they look like trees. Then they move...
Tome of Eldritch Lore: the Massa di Requiem par Shuggay, an opera that tells of the Shan's travels. It's also impossible to perform, since Azathoth would be summoned midway through the second act. The result would be nightmarish.
Weakened By The Light: Sol's electromagnetic radiation has an averse affect on the Shan's metabolism.
K’n-yani
Human-like inhabitants of the subterranean land of K’n-yan, a blue-lit cavern under Oklahoma. According to their legends they came to Earth with Tulu (aka Cthulhu), and settled underground as the surface was uninhabitable. When R'lyeh sunk, the K’n-yani became isolationist and spent millions of years underground alone. They developed a virtuous high tech civilization, but then abandoned much of it to become a cruel hedonistic aristocracy. They worship a large number of Great Old Ones, Cthulhu and Yig being the most prominent.
The Ageless: Having discovered the secret of Immortality, they have ceased to age.
Animate Dead: The y’m-bhi - one of the many slave classes used. Reanimated by using nuclear power, many were other slaves who were used by the Old Ones for "entertainment". As a result many are horribly mutilated.
Human Aliens: Very odd for a setting with very alien aliens. However, the Old Ones have the power to make themselves intangible at will thanks to their psychic powers.
Humanoid Abomination: Gyaa-yoth - white beasts with black fur on their backs, little intelligence, a singe horn on the forehead, and vaugely humanoid shape. Despite their carnivorous nature, they're somewhat harmless. They're the result of crossbreeding slaves with reptilian beasts.
The Fair Folk: The Old Ones have great powers, and amuse themselves by tormenting slaves and anyone who comes close to their surface entrances. Any outsider who enters K’n-yan can no longer leave. Visitors may be treated nicely (if lucky), but if they attempt escape...
Lost Technology: Once had an advanced industrialized culture. Then they merely abandoned machinery finding it unsatisfying.
The Social Darwinist: The ruling class - apparently they rose to power when K’n-yan developed a democratic society. Thus rose the most intelligent, while workers became exhausted and were enslaved.
Slave Race: The y’m-bhi and the gyaa-yothn. Along with them are a K’n-yani slave caste, some of which are classified as livestock.
Telepathy: Their primary means of communication, verbal speech being abandoned save for rituals.
Lloigor
Vortexes of energy that once ruled the prehistoric continent of Mu. Originally from the Andromeda galaxy, they began to lose their power while on Earth, and eventually went into hibernation. Occasionally the Lloigor can take the form of flying reptiles. Servants of Ghatanothoa.
Human Resources: Because of their weakened state, the Lloigor need to gather energy from sleeping humans. Good news is that it just leaves a person temporary drained.
Mind Over Matter: Capable of creating massive explosions and altering time with this power.
Our Dragons Are Different: Their temporary psychical forms are likely the basis for Dragons, and why there are no remains of said creatures.
Walking Wasteland: Near centers of Lloigor activity, the crime rate increases dramatically with increasingly more depraved activity.
You Have Outlived Your Usefulness: They will casually destroy any of their human servants if they even prove the slightest inconvenience.
Mi-go, AKA Fungi from Yuggoth
Crab-like fungi aliens that come to earth for mining.
Alien Abduction: In the Call of Cthulhu game, the Mi-Go are the ones who carry these out.
Brain in a Jar: How other subspecies that can't breathe in space travel. Also fond of doing this to humans.
Cool Gate: The Devil's Steps in the Severn Valley houses a portal to Yuggoth. Fortunately , a human can use the gate as it reconfigures the traveler to survive its destination. Unfortunately, Pluto houses things far worse than Mi-go...
Grand Theft Me: They sometimes implant the brain of one of their kind in someone's skull.
Hive Caste System: At least one sourcebook for the RPGs divides the Mi-Go into three castes: warriors, workers and scientists.
Lightning Gun: In the role-playing supplements The Stars Are Right! and Terror from the Stars describe the Mi-go as having Electric Rifles.
Plant Aliens: They seem to be made of some kind of fungus.
That's No Moon: Call Of Cthulhu sorcebook Malleus Monstrorum mention how Mi-go harvest flesh of the Outer God Ubbo-Sathla and use it to construct bio-mechanical super weapon capable to travel through time and space, the living moon Charon AKA Pluto's moon.
Nightgaunts
Thin, black humanoids with large wings, rubbery skin, and barbed tails. They are the servants of Nodens, and Brian Lumley had associated them with Yibb-Tstll.
Based on a Dream: A nightmare Lovecraft had inspired these creatures.
Tickle Torture: Using their barbed tails, they tend to do this to the people they capture.
Shoggoths
Vile gelatinous creatures bio-engineered by the Elder Things. They are massive, amorphous, with eyes floating on its tar-like body, and emits green light. They are able to create organs at will.
Blob Monster: Shoggoths have no real shape. They can adjust their form into whatever is practical for a specific task, but usually resemble large gelatinous blobs sometimes depicted with tentacles and/or multiple eyes and mouths.
Dumb Muscle: Meant to be living construction equipment/servants.
Servant Race: Shoggoths were bred by the Elder-Things since in theory they were the perfect servants, and who can blame them? Their capability to easily change shape as needed meant that they were capable of a nearly limitless variety of tasks. Unfortunately that also made them formidable adversaries when they developed intelligence. The Deep Ones might also use Shoggoths (they were referred to in The Shadow Over Innsmouth), possibly withe more success.
Slave Race: After gaining intelligence, and after their first failed revolt, to the Elder Things. Others (such as the Deep Ones) also use them for their bidding.
Partial Transformation: Shoggoths are versatile shapeshifters, able to create any organ they need. However, the ability seems limited, as most Shoggoths appear to be a horrendous mesh-mash of organs and black goo.
Squick: An in-universe example for Alhazred, who would not even mention Shoggoths unless he was high on drugs.
Elephantine bird-like creatures with scaly slimy skin, bat wings, two talons, and horse heads. They can be used as steeds, and serve Nyarlathotep and Ithaqua.
Call a Smeerp a "Rabbit": Also called Shantak-birds. Except for flying, these creatures have little in common with birds.
Monsters from outer space that hunger for blood. If they're seen (never a good sight), they're a gelatinous mass with a huge mouth and talons, covered in trunk-like tentacles - each one ending in a sucker.
Giggling Villain: Its presence is marked by mocking giggling sounds.
Tome of Eldritch Lore: The De Vermis Mysteriis, or "The Mysteries of the Worm". Written by Ludwig Prinn (a 15th century sorcerer), the book contains the secrets of summoning these creatures.
Tcho-Tcho
"Abominable humanoids", short and hairless, who serve the Great Old Ones. Their abode is in Burma, on the Plateau of Tsang (which is also an extension of Leng).
Culture With A Dark Secret: In T.E.D. Klein's "Black Man With A Horn", a missionary goes to investigate the group:
"... the nastiest people who ever lived ...They'd been living way up in those hills I don't know how many centuries, and whatever it is they were doing, they weren't going to let a stranger in on it".
I'm a Humanitarian: Human flesh is a dietary staple. "Bak bon dzhow" (mashed ganglia from human brains) is a particular favorite. They even have restaurants that specialise in serving ethnic cuisine to unwitting outsiders...
Our Gnomes Are Weirder: Gnome-like and depraved cannibals that can really be considered an amalgamation of Cannibal Clan, Hillbilly Horror and Yellow Peril. Making them one of the most racist things to come out of the Mythos. Ironically, the degenerate cannibalism part was not inserted by Lovecraft - that characterization was introduced by the modern role-playing game.
The Triads and the Tongs: Having migrated to America, the Tcho-tchos had created crime syndicates to continue their "traditions".
The Vietnam War: Apparently the Tcho-tcho was involved in the conflict.
Tomb-herd
Immaterial white, jellylike flopping things. They are capable of creating portals to burial vaults, where they feed off a fungus growing off bodies. Affiliated with Yog-Sothoth, as sites of its worship attract their attention. Because of their lack of substance, they have to possess statues (or someone) for their ghastly deeds.
Reality Warper: A limited variant – the Herd can warp space to turn back on itself. So if a person wants to get away from a location, they always end up at that location no matter which direction they go! However, this power has a limited range.
Temple of Doom: In Temphill of the Severn Valley there is a temple of Yog-Sothoth that exists in the same area as a local church. The Herd visits the Ancient Tomb located bellow, and the local cult goes there for worship.