Animalistic Abomination

A sub-type of Eldritch Abomination, the Animalistic Abomination is a monstrosity that resembles one animal - or often multiple - and that resemblance can range from "significant enough to recognize" to "disturbingly accurate", while still remaining definitely "alien" on the Sliding Scale of Anthropomorphism.

This type can be even more nightmarish than your average horror due to the contrast of something so thoroughly and decidedly unnatural appearing in a form "borne" of nature. Somewhat less commonly, Animalistic Abominations may actually be a direct product of their environment, which can sometimes suggest that nature itself is harboring a severe animosity towards locals... assuming you're still currently on Earth, anyway.

If you're not, consider whether or not you're confusing your abomination of choice with a Starfish Alien: Starfish Aliens are most simply adapted to a different environment from humanity and may take on more comprehensible forms for our benefit, whereas Animalistic Abominations (or any kind of Eldritch Abomination) will feel wrong no matter how much they "should" be at home - and their form being familiar to us is anything but a good sign.

Anime and Manga

 * Berserk has the Beast of Darkness, a monstrous wolf that is Guts' bloodlust and hatred of Griffith given form. It's one of the swordsman's greatest enemies, and wants nothing more than to make him submit to his darkest desires so it can permanently steal control of his body and freely indulge in its psychopathic bloodlust.
 * The Tailed Beasts of Naruto fame are dangerous monsters made of primal Chakra, and look like massive and unholy versions of otherwise ordinary animals, such as the Eight-Tails looking like a skinless ox with octopus tentacles, or the Nine-Tails being a demonic-looking fox. Most have been sealed inside of human hosts in hopes of keeping the unruly beasts under control, but this often results in the hosts going insane or having control of their bodies ripped away by the beasts possessing them.

Film

 * The titular monster of John Carpenter's The Thing is first shown in the very convincing guise of a sled dog running towards an American research station in Antarctica. When it's placed in a kennel with other dogs on-site, they immediately realize it's nothing like them and act hostile towards it, just before it transforms to attack the other dogs and absorbs most of them.
 * In Annihilation, animals exposed to the Shimmer are mutated into a form that, while recognizable, are far more alien and freaky than anything found on Earth. On the more mundane side of things is an alligator with a mouth full of shark teeth, while far more extreme is a bear with its skull exposed that can mimic the dying screams of a human it killed, and has one of her eyes and quite possibly her entire skull assimilated into its being.

Oral Tradition, Folklore, Myths and Legends
"The locusts looked like horses prepared for battle. On their heads they wore something like crowns of gold, and their faces resembled human faces. Their hair was like women’s hair, and their teeth were like lions’ teeth. They had breastplates like breastplates of iron, and the sound of their wings was like the thundering of many horses and chariots rushing into battle. They had tails with stingers, like scorpions, and in their tails they had power to torment people for five months."
 * The Bible:
 * In Chapter 9 of the Book of Revelation, the first eleven verses describe "locusts" that are summoned from the Abyss, and appeared as armored horses with human faces, long hair, scorpion tails and leonine teeth. Unlike a typical Plague of Locusts, they were sent to torment and harm "those people who did not have the seal of God on their foreheads" for nearly half a year; they are also led by the angel of the Abyss (known as Abaddon in Hebrew and Apollyon, or "Destroyer", in Greek). From Revelation 9:7-10:

Video Games

 * Undertale has one of these in.
 * Bloodborne has many, but the Cleric Beast and Vicar Amelia are among the most iconic examples. They look like massive bipedal wolves with reindeer antlers that have been starved to death, and their screams sound truly hellish. Both seem to be some form of Wendigo, with the latter introducing herself by erupting forth from the body of a seemingly normal priestess.
 * Barbas from The Elder Scrolls is a benevolent and adorable example, being a talking Big Friendly Dog with a Brooklyn accent and the best bud of Daedric Prince Clavicus Vile... as well as an aspect and the conscience of the Prince himself, who tries to keep him from screwing over anyone unfortunate enough to bargain with him. Furthermore, The Elder Scrolls: Redguard shows that he doesn't strictly stick to the form of a dog, and can be seen randomly changing forms before resetting back to his dog form. Clavicus will even comment on it, saying that he likes being a dog on sunny days, as well as many other things.
 * Since the Heartless from Kingdom Hearts are an entire race of Eldritch Abominations, the ones with more animalistic forms invoke this trope such as the Powerwilds and Bouncywilds or Pot Spiders. But even among them, there are a few that stand out:
 * Skoll, a massive wolf Heartless named after the giant sun-chasing wolf from Norse mythology. It fights by summoning packs of ghostly wolf minions, firing off powerful ice attacks, and trying to crush Sora and friends underneath a mass of darkness big enough to fill up the sky. But what makes it really special is the fact that it's the Heartless of Prince Hans himself, who's been completely corrupted by the darkness in his heart.
 * Scar similarly becomes consumed by hatred and rage. But unlike Hans, his inner darkness is so powerful that he manages to hold onto his original form after becoming a Heartless... a feat only shared by Ansem, Seeker of Darkness..
 * The Halloween Hack has the Desire Dog, which appears as a Zombie Dog in the overworld - but in-battle, the front half of its body consists of gooey tentacle-like pseudopods that it frequently uses to attack, and upon death it collapses into an array of wriggling tentacles.