Eldritch Abomination/Oral Tradition

Abrahamic (The Bible and The Quran, plus deuterocanon)

 * Obviously, God. Oh God. What happens when you combine all the Outer Gods (especially Yog-Sothoth and Azathoth), with the Eldritch turned up to incomprehensibly inconceivable levels? The "old guy" we represent in our paintings is in fact just one of many forms, The Bible gives us no actual physical description of God as such, but it is clear that his visage is not something that mortal men can comprehend. Let's try to describe:Omnipotent, omniscient, an eternal living paradox who is beyond all reason and exists everywhere simultaneously at every point in space and time, God is the All-in-One and One-in-All, connected to all existence itself - in fact the very existence of existence is nothing more than His handwave from absolute nothingness thus creating the universe for "who-knows-what-purpose", will never die and could likely claim that it had been around since the dawn of eternity to the point where even with strange aeons even Death itself will die, and has existed before time itself began and will exist long after the fabric of space and time itself has died yet He himself is bound by time, is literally the beginning and the end of all things and thus has seen the beginning of history and will usher in the end of history as well, and on top of that He never changes and is the same yesterday, today, and forever despite changing His ideas every chapter and then, and... My brain already hurts, but that's actually just a very tiny part of theological Wild Mass Guessing on what the nature of God really is.

Basically, Cthulhu is a cute little cutie compared to God. A related postulation is that His true form will Mind Rape you with its sheer eldritch glory and completely annihilate free will forever. Worst of all, He completely controls our destiny whether we like it or not. And he literally did everything. Unlike other Outer Gods, however, God at least provides perfect love, justice, and forgiveness as long as you worship and revere Him, and can even allow those who don't love or worship Him to have comfort and prosperity in their lives. He also took A Form You Are Comfortable With we all love named Jesus (then again, Outer Gods communicate with us through Nyarlathotep, and consider Jesus's true form in Revelation...), but then again, He can and will perform many nasty acts like smite and punish thee day and night forever and ever.
 * His omnipotence, combined with pretty extreme measures when dealing with evil, still makes Him a force to be reckoned with. Yeah, He's seeking to be kind, but man can He be harsh.
 * Even our best theologians don't help in describing His mindscrewyness.
 * Islam takes this bit particularly seriously; being the omnipotent, omnipresent being who created the Universe, it is forbidden to portray Him in pictures, partly at least because You Cannot Grasp the True Form.
 * In fact, just looking at His face will kill you if you do so while alive.
 * Not a problem in Heaven, which is reached after dying and with an immortal soul.
 * Except in Islam, where if you make it to the highest heaven, you will look upon His face and and experience indescribable bliss.
 * Our Angels Are Different. How different? Let's take a look.
 * The ancient depictions of angels are more like traditional Eldritch Abominations than the fluffy cloud angels we see nowadays on Christmas decorations. The cherubim (Yes, those cuties we all know today), have four faces - a lion on the right, an ox on the left, a human forward, and an eagle backward. They have four wings, with HANDS under the wings, their legs described as simply "straight", and they have hooves. Also, the eyes. Everywhere. Even in the spaces between the eyes. Furthermore, "Cherubim" means "the living ones". This means, in the eyes of the Hebrews, the most outstanding characteristic amongst the other orders of angels was that they are alive. Not so cute anymore, is it?

Contrast the Seraphim, basically cherubim with extra wings that are on fire, whose name means "Fiery Ones", and the Ophanim, that take this to the extreme, being wheels intersecting themselves while turning, also flying with six wings, somehow attached while they're turning, whose name means "Wheels". Remember, neither of these were understood to be alive by the Hebrews. Add to all this that God's guard for the Garden of Eden was a cherub armed with a flaming sword that turned in all directions. There's a reason angels would address humans with "be not afraid" or just come with a form you would be comfortable with. That they are so nice takes the abomination out, even if they are eldritch.
 * Some interpretations of Seraphim hold that their divine fire radiates a light so ineffably potent that it will SEAR FROM EXISTENCE anything that approaches too close, including, presumably, lesser angels. That's still nothing compared to God Himself, for whom the Seraphim are the mundane equivalent of matches, basically shining as tokens of His glory.
 * Seraphim are also described as dragon/serpent like (which led some experts to believe that they are loosely based on the goddess Wadjet from Egyptian Mythology, which is also a fiery snake). They consistently have six wings, and one of them is used to cover their feet. In spite of the fact that they are snake-like. Try figuring that one out.
 * It gets worse. The Book of Revelation implies that there are angels so powerful and evil, that God locked them up in a bottomless pit because He didn't want to bother with them. A bottomless pit; that means a pit with a definable end would not be enough to contain these monstrosities. And they're going to be let out one day, at The End of the World as We Know It. Revelations also claims that the Seraphim loyal to God have wings covered with eyes.
 * And on that note, another named Seraphim is Metatron the Record Keeper, an angel whose job is to record the lives of all mortals who have ever lived. Catholic scripture (as in, scripture outside the Bible) claims that for each mortal's life he records, he gains one eye and one tongue, meaning he has one of each for each mortal who has ever lived. Yeah, that does sound like something Lovecraft might have thought up.
 * Ironically, notably and deliciously subverted with demons, all of which are said to be inferior to humans and powerless against them, although their parasitic powers are exceptional. Indeed, we are probably seen as eldritch abominations by demons, considering that, allegedly, the first example in this section has given humans a blessing and a chance at salvation while cursing demons to an eternity of suffering.
 * Thomist philosophy's angels aren't weird-looking-because they have no appearance, being pure ideas. This concept was pretty much borrowed from Plato's Theory of Forms (Theory of Ideas). But the Platonic Ideas still definitely fit the "weird psychology" part. They have no need to reason or learn, because they know everything that they even can know, simply as a function of their self-awareness. They are timeless and infinite, and have no feelings; though they have enormous power to influence the world, it isn't by "action", as humans would understand it. The Real World as we see it is in fact just a shadow of these Forms, whom You Cannot Grasp the True Form. The perfect Idea of blueness "is projected" on what we "perceive" as a blue object. It's like The Matrix, only the Real World is not this real world but instead is mind screwy. Also, the most powerful of all angels, the supreme created entity, second only to God / The Form of the Good Himself? Satan, the Idea Of Evil.
 * Islam also holds the "Eldritch Abomination" view of angels. The Prophet Muhammad was terrified when he saw Gabriel in his true form; God, through Gabriel, spends the first few verses of the Sura (chapter) Al-Muddathir calming him down.
 * The Nephilim. The gigantic offspring of  Watchers and human women. They are offhandedly referenced in  Genesis, the deuterocanonical Book of Enoch describes them as being "3,000 ells" high. For reference, 1 ell is equivalent to 1.143 metres.  So the Nephilim are 3.429 kilometres high. They are also stated to have "turned against [their parents] and devoured mankind". They are also stated to have devoured one another's flesh, drank their own blood, and to have engaged in "sin against birds, and beasts, and reptiles, and fish".
 * Behemoth and Leviathan are also worthy of mention. It is to the world's great benefit that these two great beasts are mortal enemies, since it is said that their offspring would be the end of the world.
 * In the original Jewish lore, they form a trio with the Ziz, a gryphon-like bird whose wingspan would block out the sun. The Ziz once threw away a rotten egg, and thirty cities were flooded by the liquid of it, and 300 cedars were broken by the shock of the falling egg. If the Ziz would stand in the middle of the ocean, the water would only reach his knees. Eldritch enough.
 * Leviathan is also said to be 300 miles long, and that is on top of breathing fire, having impenetrable scales, and glowing eyes. Behemoth is descibed so vaguely that all that is clear is that it is a herbivore, incredibly strong, and invulnerable to anything that is not omnipotent (i.e. God). Not being able to describe it properly is a sure sign of an eldritch abomination.
 * Psalm 104 refers to the Leviathan as being an entity which God created to play with. Presumably because nothing short of an Eldritch Abomination would be any fun?
 * It gets better. Part of the prophecies concerning the End of Days is that these two beasts will kill each other... and afterwards the righteous will eat them in a great feast. Did You Just Eat Cthulhu?
 * One of the strangest parts of Revelation is its descriptions of Jesus. These include a man with a head and hair that is pure, snow white, eyes of fire, and feet of brass, with stars in his hands and a sword from his mouth who shines like the sun, and a lamb with a slit throat, seven horns and seven eyes. Either Jesus becomes a Humanoid Abomination, or he's unlocked the ability to turn Super-Saiyan.
 * Some Christians have interpreted several verses, such as many in Corinthians 15, as that Yahweh changed mankind's original shape into that we have now, and that we will regain the original form when we meet Jesus again. Judging by the two forms Jesus takes in Revelation, we will most definitely become those eldritch beings that caused Instrumentality. A rarely used trait of Cosmic Horrors is the ability to mutate surrounding lifeforms by its very presence.
 * Revelation is full of them. The Beast, with its seven heads and ten horns, is one well known example.
 * Satan becomes one in Revelation as well; he is described as a "great red dragon" with seven heads and ten horns, so powerful that a single swipe of his tail sends one-third of the stars falling out of the sky. This is from the description of the War in Heaven between Satan and Michael, each with their own army of angels. A common interpretation is that the fallen stars are the fallen angels that sided with Satan. So a third of all angels fell.
 * Remember, the Book of Revelation (and indeed, the entire New Testament) was originally written in Greek. The Greek word "aster" does not mean, "naturally occurring nuclear fusion reactor." Rather, it means "celestial body." "Angel," by contrast, means "messenger." Thus, "aster" is a physical description, whereas "angel" is a job description.
 * In the beginning of Revelation, one of the first things St. John notices upon arriving in heaven is four gigantic "living creatures," in the approximate shapes of various animals--an eagle, an ox, a lion, and a human face-- each one having multiple wings and completely covered in eyes, even under their wings. Also, they can speak, which tends to knock people over. We're not exactly dealing with Fluffy Cloud Heaven here.
 * The Quran gives us The Beast of the Earth. In addition to having a name to run away from really fast, it was sent by Allah, andits physical form is not described. Its coming will heraldThe Last Day. The book of Jami' Al-Tirmidhi features a Hadith describes it as wielding Musa(Moses)'s staff, king Sulaiman(Solomon)'s ring, and says that it will "brighten the face of the believer" (whatever that means), and will use the ring to brand disbelievers; so as to tell Muslims and Non-Muslims apart. Yes. It Judges You. The book Tadhkirah describes the Beast as having the head of a bull, the eyes of a pig, the horns of a stag, the ears of an elephant, the neck of an ostrich, the chest of a lion, the fur-colour of a tiger, the haunches of a cat, the tail of a ram, and the legs of a camel. It also states that "Between each pair of its joints is a distance of twelve cubits".
 * Just to clarify, 12 Cubits= 5.4864 Metres.So it's technically not 50-feet long, but still very, very big.

Classical

 * Khaos, when portrayed as a deity and not a giant void that reality came from (and one of the Protogenoi, who aren't just older than the Olympians, they are older than even the Titans! If Greek myth is paralleled to Lovecraftian myth, then the Protogenoi are the Outer Gods and the Titans are the Great Old Ones) is described by Ovid as "rather a crude and indigested mass, a lifeless lump, unfashioned and unframed, of jarring seeds and justly Chaos named." Also, Chaos is the mass on which all the other gods (and therefore the cosmos, with the gods being Anthropomorphic Personifications of universal laws) emerged. A lumpy, crude, unframed mass, creating the universe as we know it? Throw some tentacles on it, put it in the center of infinity and call it Azathoth!
 * The rest of the Protogenoi starts with the hermaphrodite Phanes Protogonos who was born from the Orphic Egg, which had the serpent Ophioneus wrapped around it . The protogenoi also includes Gaea, and her husband Ouranous , when he isn't also her son that is. Tartarus, which came inhandy when Ouranous found that the first batch of children to come from the union of two Incestuous Abominations were equally abominable, see below. Before Neptune, Oceanus, Pontus and all the other Greek Gods and Goddesses of the sea/ocean et al, their was Thalassa, sometimes she is Gaea's daughter, sometime her granddaughter by Aether and Hemara , the counterparts of which Erebus and Nyx are also a couple.
 * The first children of Gaea and Ouranous were the Hecatoncheires (meaning The Hundred Handed Ones) had one hundred arms, one hundred hands, and fifty heads with no further details of their appearance given. Compare that to Ravana who had only ten heads and twenty arms, though even that is enough to put him on the border of this trope. Now try and imagine what the Hecatoncheires looked like. You can't quite do it can you? Nope, the only name the greeks could even come up with for these things was basically to call them "those things with one-hundred hands" which was about all we humans could comprehend of them. Well here is what D&D came up with when they asked their artists do draw one.
 * It is well worth noting that the Hecatoncheires were on the Greek gods' side against the Titans, throwing a hundred mountains in a single salvo apiece - much like having a living artillery piece as an ally.
 * Actually, if you've seen Tengen Toppa Gurren Lagann, visualizing them isn't that hard. We don't know if they have bodies, now do we? All we know is tons of heads and tons of hands.
 * Typhon, the youngest and most powerful of Gaia's offspring. Lower half consisting of serpent coils, a human upper half that reaches the stars, arms that spanned the East and the West covered with live dragon heads, a body covered in mighty wings, and eyes that shot forth flames. When it first appeared, all of the Greek gods except Zeus ran like hell. And even Zeus, the most powerful god of them all wielding his mighty thunderbolts in battle, lost the first round against Typhon (by Typhon STEALING ZEUS'S SINEWS and HIDING THEM), and barely managed to seal it away under Mount Aetna in round two. Before it was sealed away, Typhon also fathered most of the monsters present in Greek Mythology, such as Cerberus, the Sphinx, Orthus, the Nemean Lion, the Hydra, Ladon, and the Chimera (their mother Echidna might also fit the bill). And how did Gaia give birth to this beast? By sleeping with Tartarus, a.k.a. the Greek Underworld. The Earth slept with ancient Greek Hell to give birth to a monster that frightened the gods themselves.
 * It Gets Worse. In some versions, he has a hundred "dragon" heads on his shoulders, which he can rip out to create a fully-grown monster from it; just one of those was enough to guard an imprisoned Zeus from the other Gods.
 * Although the fact that Zeus was willing to fight it says volumes for the guy's courage. And his re-entry into the fight was pretty awesome in its own right, too - he jumps off Olympus and started hurling thunderbolts before the inevitable end-battle finale of beating the thing over the head with an entire mountain, hitting him so hard that he sent him all the way down into Tartarus. Yes, that's right: Zeus clubbed Typhon into another world... with a mountain as his club and the other world being the Greek equivalent of Hell. There's a reason why he's King of the Gods.

A different version upgrades it from Mount Etna to the whole island of Sicily - Typhon was standing in the sea before being hit. And as mentioned above, the blow didn't kill him but only trapped him underground - the flames, smoke, and lava of the volcano Etna come directly from his mouth.
 * His mate Eckidnai/Echidna is nothing to sneer at either, roughly equivelent to fellow Eldritch Abominations Tiamat and Leviathan in her role as a Goddess Beast of the Primordial Sea, Mother of a Thousand Young, and bigger and badder than any of her children with an appetite to match. Basically all three of these mothers, and every other lesser known version of this common theme, are Cthulhu, Shub-Nigurath and Yog-Sothoth all rolled into one nasty package.
 * The Earth produced another one when she slept with her own grandson Poseidon, unless she is one of Ekhidnai's and Typhon's children that is. Charybdis was apparently once a beautiful naiad but was transformed by Zeus into a horrible and utterly inhuman monster. According to The Other Wiki, in some versions she is a huge bladder of a creature whose face was all mouth and whose arms and legs were flippers that belches out whirlpools while in others she is a giant whirlpool. When forced to choose between Scylla and Charybdis, Odysseus quickly chose Scylla for good reason.
 * Charybdis is (after Homer, the autor of the Illias and the Odyssee) a giant whirl of water that sucks three times a day enormous amounts of water devouring entire fleets in the process and spits it out with a loud roar. Skylla is a monster with numerous heads which also destroys ships by eating the crews... The trick behind passing those two monsters is to ship exactly between them. Unfortunately Odysseus gets too close to Skylla the first time since he wants to avoid Charybdis and loses many comrades to Skylla. Later on his fleet is utterly destroyed by a storm and Odysseus, who's holding onto a part of a ship for his life, gets pushed back to Skylla and Charybdis and only survives to Charybdis since he manages to catch the branch of a tree on the rock hanging over Charybdis and waiting for Charybdis to spit out its water to get something to float on...
 * According to some versions of the story of Dionysus, a god's true form will kill a mortal in front of him/her, as evidenced when Zeus appeared in all his glory in front of Semele, Dionysus' mother, who was incinerated in the process (Zeus' "true form" was apparently a powerful tempest of thunder and lightning, since they were his main powers). This happened because Hera, jealous of the affair Zeus had with Semele, tricked Semele into asking for it when Zeus swore to grant Semele anything she'd ask for, despite Zeus' pleading not to due to the aforementioned consequences.

Norse

 * Ymir, a frost giant and the first living being. He was so big that the earth was made out of his corpse (the soil from his flesh, the stones from his teeth, the grass from his stubble, etc). This means that he was at least as big as the planet.
 * Fenrir, or Fenrisúlfr - the Big Badass Wolf among Big Badass Wolves and one of Loki's three monstrous children by a female jötunn (often translated as "giant", despite not every jötunn being especially large). Fenrir is prophesized to break his binds and "go forth with his mouth opened wide, his upper jaw touching the sky and his lower jaw the earth, and flames will burn from his eyes and nostrils"; during Ragnarök, he will aid the forces of Surtr alongside his sibling, the World Serpent (who is another example discussed below), and consume the King of the Æsir, Odin.
 * The Æsir raised Fenrir among them while devising a plan to try and permanently bind the ever-growing canine - they coaxed Fenrir into testing fetters through promises of fame for his strength, and when placing the dwarven-made Gleipnir Fenrir suspected there was trickery afoot, but allowed them to test it on the condition that Týr place his hand in Fenrir's mouth as a pledge of good faith. As the only one who had been courageous enough to approach and feed the wolf, Týr obliged - when it turned out that Gleipnir would hold, so did Fenrir, and off came the hand. The gods then thrust a sword into his mouth when he tried to bite them, holding it opening and gagging him; this caused him to produce horrible howls as saliva ran from his mouth, which formed the river Ván (Old Norse "hope"), and so he would remain bound until Ragnarök comes.
 * Fenrir's sons, Sköll and Hati Hróðvitnisson, are each a Big Badass Wolf in their own right, and eternally chase the sun and moon respectively across the sky; one of the signs heralding Ragnarök is Sköll eating the sun and Hati swallowing the moon. Then, the stars will then disappear from the sky, the earth will shake violently, trees will be uprooted, mountains will fall, and all binds will snap – and then their father will break free...
 * Jörmungandr the Midgard Serpent, one of the monstrous offspring of Loki and a giantess. Starting out big, he grew so large that he can encircle the world, and sleeps at the bottom of the ocean depths while keeping his tail in his mouth - one of the signs of Ragnarök is finally releasing his tail, then causing to seas to flood as it thrashes onto the land and fills the water and air with its poison. Joining Loki and his other children in confronting the gods, Jörmungandr's role in the conflict is a battle with his Arch Enemy Thor that ends in a Mutual Kill - the hammer-wielder successfully slays the Serpent, but is felled by his poison after walking nine steps.
 * Nidhoggr. Sweet Baldur, Nidhoggr. It chews the roots of Yggdrasil and has human corpses as snacks... It is said to even be able to survive Ragnarok. Oh and to put its size in perspective of scale, Jörmungandr may sit in an ocean, surrounding all of midguard in its coils, but that ocean still just sits in on the end of one branch of the World Tree, while Níðhöggr's massive form encompasses the entire rootsystem of the World Tree itself.
 * There is also an eagle called Hresvelgr at the top of the World Tree, and is the enemy of Nidhoggr (implying that they are of about equal size and power) and he has a hawk named Veðrfölnir sitting on his head.
 * Ratatöskr is the being that carries messages between Nidhoggr and the Eagle. Commonly taken as a squirrel, albeit a squirrel large enough to climb up and down the World Tree with ease. Its name comes in two parts, rata- meaning; climber, traveler, borer, gnawer - and -toskr meaning; tusk (or at least tooth) thus Ratatöskr can be interpreted to mean the Climber Tusk, Bore-Tooth, Drill-Tooth, or Tusk the Traveler.
 * Dáinn, Dvalinn, Duneyrr and Duraþrór are Harts or Stags also said to live among the branches of Yggdrasill.

Asian

 * Amenominakanushi, who is considered a sort of Supreme Being in some forms of Shinto, and considered the center of all creation; all other kami (often translated as "gods", though the more fervent practitioners consider this a Berserk Button) are considered a part of him. Kami themselves could be considered Eldritch Abominations as well due to just how vague the definition of "kami" is, with descriptions ranging from anthropomorphic to amorphous. Shinto is an animistic religion, so everything in the universe has a kami, including humans. The kami also symbolize the forces of nature, the cosmos, and the laws of physics, etc. When you put that all together, that means that the supreme deity of Shinto did not create the universe, no, it is the universe itself! He is an Eldritch Abomination consisting entirely of millions upon zillions of lesser Eldritch Abominations, including us. Think about it. Interestingly, he is only ever mentioned in the Japanese creation myth.
 * There's also the relatively obscure Japanese star-god Amatsu-Mikaboshi (literally "August Star of Heaven") also called Ame-no-Kagaseo ("Brilliant Male") who most likely qualifies, given the two rather... curious passages in the Nihon Shoki that mention it, both of which constantly refer to it as "the evil kami" - a major Out-of-Character is Serious Business moment considering Shinto's usual reluctance to morally judge things as "evil" outright as opposed to merely "impure" or "unclean" - and seem to suggest that at least three major deities - one of whom was the symbolic founder of martial arts - were required in subduing it. And that's not even getting into the more dubious sources, some of which seem to imply that the August Star is less a spirit per se than a malevolent force that predates creation.
 * Hundun, similar to Khaos above, is a monster formed from the remnants of the proto-world that was not shaped into the ordered universe in Chinese Mythology. Interpretations of what he is vary: he is sometimes an internal organ-less celestial dog, a faceless giant, a sentient force of nature or even just a huge lump of flesh. All are Lovecraftian, but he is usually depicted as quite nice. In one story, two Emperors, Shu and Hu, thought that since they had holes in their bodies (eyes, mouth, nostrils, etc) Hundun should have them as well. They thus drilled those holes in Hundun, killing him in the process. In other words, Hundun was an Eldritch Abomination that got punched out by overzealous public servants.
 * Hindu Mythology
 * Ananta Shesha, lord of all nagas, is gigantic serpent with thousand heads. So huge that it can hold all the planets on the hoods. Not only can it spew venom but also breathe fire. It's also one of few beings that will remain after the destruction of universe, true to its name, Ananta - Infinity. It's good thing that Shesha prefers to sing and praise the glories of Vishnu, who sleeps on its back, rather than play this trope straight.
 * Also in Hindu Mythology we find Krishna, in the 11th chapter of the Bhagavad-Gita, gets a description befitting any great old one: an infinite number of mouths, an uncountable number of arms holding an infinite variety of weapons, fiery breath that destroys the entire cosmos, and so on. This is the main hero in several versions of Hinduism.
 * In fact, most physical depictions of Hindu gods are very eldritch. Add to that how the whole pantheon of Hinduism consists of very microscopic aspects of the supreme god (Brahman, which is what happens if you took Yog-Sothoth and the already eldritch Biblical God above and turn the "all-in-one-and-one-in-all" aspect up to even more inconceivable levels), and their own respective aspects, and it all gets so Mind Screwy that you'll need some kind of a chart to sort it all out.

Middle Eastern

 * Mesoptamia:
 * Babylonian mythology gives us some frightful critters, but the (literal) mother of all of them is Tiamat. An Explosive Breeder made to symbolize the primordial sea, her exact appearance is unknown. Later depictions portray her as a dragon or serpent-type creature, but the most ancient portrayals described her form as including a tail, thighs, "lower parts" (which shake together), a belly, an udder, ribs, a neck, a head (skull, eyes, nostrils, mouth, and lips), and insides (possibly "entrails," i.e. a heart, arteries, blood, stomach, womb... and other organs) also. She was big enough for innumerable gods and monsters to live inside her.
 * Tiamat and (possibly) Apsu and Mummu from Sumerian myth, especially the Enuma Elish, seem to fit the bill pretty well (the multi-headed dragon shtick is probably an invention of Gygax and Arneson).
 * To give an idea of how monsterous Tiamat was, one interpretation of the Enuma Elish depicts a battle between her and Marduk, an invader of her domain. By the end of it, Marduk slays Tiamat by decapitating her, making her "upper half" (her skull) into the earth and her "lower half" (her tail) the sky.
 * Egypt:
 * Apep, or Apophis, from Egyptian Mythology was a gigantic serpent-demon that embodied chaos and darkness. Every night it tried to eat Ra as he passed through the underworld, and every night Ra killed it- but it always came back. Sometimes it was strong enough during the day to temporarily consume Ra before his attendants cut him free again (this was the Egyptian explanation for solar eclipses). Prior to the demonization of Set, Apep was the canonical ultimate evil of Egyptian Mythology, and there's no solid evidence that it was ever worshipped as a positive force. There were temples in Egypt dedicated to the worship of Apep, but it was more along the lines of praying "Please, please, please, please do not let this monstrosity ever win." It was sort of worship AGAINST Apep.
 * Nut/Nuit/Newet/Neuth, primordial goddess of the sky, and EVERYTHING in it. She separates the heavens from the earth, eats the sun and the moon, and sometimes appears in the form of a cow.
 * Geb, primordial god of the earth. His laughter creates earthquakes. Usually depicted with a snakes head, or as a ram, bull or crocodile. With Nut he fathered many of the more famous Egyptian Gods.
 * Shu is the father of Nut and Geb and god of the air. Artwork and legends often have him seperating his children.
 * Nu was the Primordial Egyptian deity of the watery abyss and was usaully male, but could be the female Naunet or the male Nun (not to be confused with Nuns-N-Rosaries Nuns). Nu's repressentations varied in more that just gender, ranging from the animal (frog, snake), the humanoid (blue skinned old man), somewhere in between (frogheaded man, snakeheaded woman), and the abstract (sacred lake, underground stream).
 * Other:
 * Arabian legends (not the Quran) have fun beings like Kujata, an immense bull with all sorts of reduplicative organs, especially eyes, that carries the world on its back. It stands on the back of Bahamut (which is Arabic for "Behemoth"), an even larger fish with many of the same properties. Jorge Luis Borges' Book of Imaginary Beings mentions a legend that states that even Isa (Jesus) passed into unconsciousness upon seeing Bahamut, later telling God that he did not know what he saw.

Other

 * Nautical Folklore: The ocean. Be respectful to it and it will feed you and make you rich. Disrespect it and it will drown your homes. Or just makes sure that you will never be heard of again.
 * Tau and his offspring from Guarani Mythology.
 * There's a reason the Native American Mythology page lists all the Cthulhu tropes, all of them dedicated to the Lakota.
 * Lots of people view Aztec mythology as being the worship of a bunch of Eldritch Abominations due to copious (though likely exaggerated) Human Sacrifice. But the purpose of all that sacrifice was to keep the Aztec gods (especially the sun/war deity Huitzilopochtli) strong enough to defend our world against the depredations of the horrific Tzitzimime--skeletal, spider-like star demonesses with flint blades for tongues and rattlesnakes for penises. (And yes, they were still considered female.)
 * Even putting their bloodthirstiness aside, the Aztec pantheon is exceptionally strange and alien, even by mythological standards. Most of the gods had many, many different names, forms, appearances, roles, and general alter egos, to the point where it's often unclear whether two gods were considered separate entities or not. (Even archenemies Quetzalcoatl and Tezcatlipoca are not immune to this; Quetzalcoatl was sometimes called, "the White Tezcatlipoca.") They'd actually destroyed and remade the world four times before this one (which has to be some sort of record), going through four different suns in the process, and many of them took forms of the "hide under the bed" variety, often involving skeletons, Biological Mashups, things being substituted for body parts that really weren't meant to be, and lots of feathers and obsidian blades. Plus their names all look totally unpronounceable if you're not familiar with them. After all that, copious requirements for Human Sacrifice almost seem like an afterthought.
 * The Flying Spaghetti Monster, according to its worshippers, is the omnipotent, invisible, undetectable creator of the universe... who just so happens to look like spaghetti and meatballs. His spaghetti-and-meatballs form also resembles Azathoth. His noodly appendages guide us all.
 * Some cryptids are weirder than others. The more mundane ones are often theorized by believers to simply be prehistoric creatures that lived far past their expiration date, such as Bigfoot and Plesiosauresque lake monsters like Champ and Nessie. Then there's the legendary Mothman of Point Pleasant, which is so bizarre and alien that it can't possibly be of this world. It's a shadowy black humanoid creature with hellish red eyes and a ten foot wingspan, and contrary to its name looks less like a moth and more like an owl from Hell. It could reportedly fly fast enough to keep up with and even outspeed cars going about 100 miles per hour, and yet was rarely ever witnessed flapping its wings. Nobody has been able to describe what its face truly looks like, because the unlucky few who got a good look at it were overcome with a crippling sense of terror and psychological distress. And despite its love of chasing and terrorizing people, believers view it as a benevolent protector trying to warn people of impending doom, since its original rash of sightings led up to the Silver Bridge collapse of 1967 while others claimed to have seen it prior to the destruction of the Twin Towers during 9/11 and the Chernobyl nuclear disaster.