Tech Infantry, as a spinoff of the Old World of Darkness (see above under Tabletop Games), also has the Tszimisce clan, but their Viscissitude abilities are weaponized for soldiers of the Black Hand. These abilities are also retconned into being partial but progressive possession by the Soul Eater aliens from the planet Fieras VI, who eventually transform their victims into new Soul Eaters and completely take over their minds.
Amusing fact: This isn't actually a retcon as such, because the origin story of Vicissitude as given in the much-reviled supplement Dirty Secrets of the Black Hand is this, except replace "alien virus" with "spirit virus from the netherworld." That idea was retconned in revised edition, so Tech Infantry is retconning the Retcon.
In New Vindicators most of the superhumans are fairly normal looking, with the occasional ape person, or winged girl, but that can sometimes be a good thing. Even ancient Nephilim like Apocatastasis, who's freakishly tall and has twelve fingers, aren't that bad. But Bulwark actually has it fairly bad-he's a rock man, like the Thing, only played a little more straight. So no eyes, no functional nose, no sense of touch-'seeing' through vibrational senses, he's a mutant freak among mutant freaks.
Parodied in Homestar Runner: An Easter Egg in one of the Halloween specials shows the character Stinkoman (a character who is a walking anime parody) dressed up as Speed Racer for Halloween, and he comes up to 'your house' to get candy. One of the treats you can give him is a can with the word "Akira" printed on it. Guess what happens when you give that "Treat" to Stinkoman?
Gaia Online's Timmy experienced this trope in an Ugly Cute way after his legal guardian sealed him in a barrel of toxic waste just to see what would happen.
It says something that even Timmy is grossed out by the Penanggalan from the Nightmare evolving item. "It even has a cute female companion— eeeeeugh never mind I think I have to go lie down..."
There is a well circulated picture called Lotus Boob. The image of a lotus superimposed over a human areola and its implications of burrowed parasites is more than enough horror. Thank God that it's fake.
There's an email on Snopes with a .jpg attached of human fingers with lamprey mouths Photoshopped onto the pads. It's meant to be a joke: too much typing and mousing will wear holes in your fingers, har har!
The infamous Goatse. How is that physically possible.
Encyclopedia Dramatica uses it on the 'kittens' page.
Whateley Universe. Horror author Michael Waite is dying of cancer. Oh no, that's just what the doctors think. It's much worse than that. After he 'dies', he wakes up in the morgue. For starters, he vomits up his own internal organs. It turns out the reason he was such a good horror story writer is he's not fully human to start with.
Every single character in Ruby Quest. (Minus Bella, that is) Some of them aren't particularly obvious — Red, for instance, looks perfectly normal in his first appearance. And then he laughs. Others, though, are so twisted you can barely tell what they once were, including Stiches and Number Six. Oh dear god, Number Six...
Many of the "powers" in Survival of the Fittest Mini site spinoff SOTF: Evolution fall into this. Some are pretty "standard" as powers go, such as solar-poweredSuper Strength and invisibility, "memory absorption", Telepathy, and control over electricity, while others are pretty pathetic. Others, however, include things such as mold growing from the mouth and a character developing cat-like claws that are poisonous. The most notable one, though, goes to Johnny Marsh's "power", in which his skin is invisible, but the rest of him (muscles, organs, etc.) aren't. This means that his muscles are completely visible like an anatomical model. This receives a Lampshade Hanging when the scientists puts a full-body scuba suit on him to avoid him scaring the other subjects and interfering with the research. And then there's Billy-Jay Clarke's death in which he suffers a power malfunction, causing his eyes to catch fire and melt out of their sockets...
Worm: Mannequin of the Slaughterhouse Nine turned himself into a puppet-like monstrosity whose internal organs are all housed in seperate transparent cases, all attached to a long-limbed body with ball joints at every joint.
Bonesaw, also of the Slaughterhouse Nine, as a tinker who specializes in organic bodies, might as well be a Factory''.
Grue got a taste of this when Bonesaw disassembled his body and positioned the various organs, blood vessels, and nerves across the interior of an industrial freezer while keeping him alive and conscious.
The more extreme Case 53's fall under this trope, sometimes even referred to as "monstrous". Sveta for example is a face surrounded by a mass of tentacles that instinctively attack anybody who approaches her despite her own intentions.
This, other than death, it causes your blood to turn to crystal and go through the skin. According to the story, albeit vaguely, it seemed to come in variation but in the most extreme cases the person is already dead and barely recognizable.
The works of Karl Persson are a little like what you'd get if you combined the brains of H. R. Giger and Sigmund Freud, and soaked the result in a bucket of liquid LSD.
In The Salvation War, while Angels (like demons and "second Life" humans) have a healing factor. The angels sent to Michel's concentration camp find out horribly that growing back does not mean growing right. The Angels who were nuked suddenly were less "angel" and more "Angel shaped cancer tumors".
In The Wanderer's Library story Abundance, a stranger feeds a starving village by causing select villagers to grow new limbs and other meaty appendages, which they then cut off and eat.
Killer Monster describing how he tortures his victims in 'The Camping Webisode' of DSBT InsaniT.
The Cartoon Man parodies typical Body Horror scenarios. Instead of some kind of horrific monster, Roy turns into a hyperactive cartoon character with giant eyes and White Gloves. It's still rather horrifying for everyone involved.
From the twisted mind of Eyesglowyellow comes the Metokur chimera who — in the first two stories it appears in — turns the main character's head into a penis and another character into duct tape.
In The Saints, corruptedghosts are often heavily disfigured, either from Self-Harm or from other corrupted ghosts. Thorolf, the one corrupting the ghosts, is very decayed, with most of his skin rotting away.
Kalia's One-Winged Angel form in Dreamscape where 8 long arms with golf club-shaped hands come out of her back, as well as two smaller legs come out of the sides of her knees!
In the "Beau and the Child Snatchers" chapter of Vox and King Beau, Beau encounters a (presumably) once-human child who has been kidnapped by a woman who lives in his realm. The child is described as not only missing his jaw, but being starved and malnourished with visible ribs and skin covered in "pus-filled sacs" and "bony growths".
Played for Laughs in Monster Factory, where hosts Justin and Griffin McElroy abuse video game character-creation systems for fun and profit. Very basic examples include a character in The Sims 4 whose head is approximately 4 inches wide.
From Killerbunnies, we have Io McMorrison◊ and the fact that some if not all of her teeth grew through the surrounding tissues of her mouth.
Discussed and played for laughs on Steam Train in Dixie Kong's Double Trouble Part 10. Ross speculates about how horrifying it would be to turn into an elephant...and suddenly remember everything.
Will It Blend?: In the episode "Tom's Hand", Tom decides to blend his own hand at the request of several viewers, so he is seen pulling off his own hand! The blended mix is red with blood and crumbled up bones and he warns the viewers "Don't drink this!"
The Scientifically Accurate parody of Catdog is this. 
The necromancer Sawyer in Void Domain is fond of creating creatures that would fit under this trope.
In Season 1 of Within the Wires, The Narrator uses an autogenic exercise to reveal and explain hidden, standard-issue Cybernetic implants to a research hospital patient. A hollow between the patient's lower left rib and left hip is occupied by a mechanical creature with "many legs". It collects their memories. Later the Narrator explains replacement devices typically issued to patients of the Extensive Studies Lab, and elaborates on the surgical wounds incurred in gory, explicit detail. The "creature" was a black box that monitored the patient's vitals, now replaced with a transmitter used to track the patient should they try to escape.
The strange creature that pops out of the egg in the third DHMIS is quickly smashed by the Duck Guy, leaving the cracked egg full of gore.
Digital glitches in the fourth episode leave the main character's in horrible, distorted forms. Also, Colin's "Digital Mind" is some sort of squishy, red substance.
Heroes Save the World: The story practically begins with this. In chapter one, Simon, who is able to see how people are going to die, has a vision of "a forest of bodies, suspended, twisted into grotesque, wiry shapes." Simon dubs them "Giger trees."
The IT's in HELP_tale (An alternate universe of Undertale) are a very good example of this trope.
In Undertale, it is explained that there are hundreds of different timelines that continually branch off of each other with each possible choice that the player is given. It is also explained that when these branches split too much, they stop and collapse into each other. This is exactly what happened in HELP_tale. The collapse inadvertently created grotesque beings (called IT's) that are the various characters from their respective alternate universes smooshed together into one entity.
An extreme example is the character Sans: because of the number of AU's devoted to him, the timeline had to combine hundreds of thousands of separate people into one singular entity. This caused so much corruption that his IT isn't even humanoid. Its a circle.◊ Luckily its in black and white and pixelated, so its not as bad as it could have been.
Daisy Brown: Alan is a genetic monstrosity created by Daisy's father, and is not a pretty sight to look at. He starts out as simply a gray limbless head and body with milky blind eyes and More Teeth than the Osmond Family. Then, he gets worse over time, with root like growths coming out of his skin. Because he grows so fast, Daisy has to literally sew him together after a while. Oh, and he can see and talk now.
Later, we get the lovely image of the final boss slowly feeding off of her love interest's body using cables embedded into him. He eventually figures out that removing the cables weakens the system, but this comes at a great physical cost to him as well, bleeding profusely from each hole in his body.
The YouTube channel "Chubbyemu" features a medical doctor who takes viewers through various medical case studies. The videos have clickbaity titles like "A Boy Ate 25 Laxative Brownies In 1 Hour. This Is What Happened To His Kidneys", often paired with gross medical images. The videos themselves are coldly-presented narratives in which we are told in excruciating detail exactly how badly our bodies can go wrong and fall apart, often in ways we don't expect. Of course, the stories he tells are very rare edge cases and most of the time if you get ill you'll be fine...but if you're one of these unlucky (or Darwin Award-contending) souls, God help you.
This creepypasta, as the title directly states, about a young woman who slowly develops zippers on various parts of her body.