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.
The SCP Foundation has so very much that trying to list them all would involve recreating half the site here. Reading random articles for any length of time is bound to make your skin crawl. Virtually any SCP labelled "transfiguration" will involve some degree of this trope.
SCP-149 ("The Blood Flies"). These mosquitos inject a virus that changes human cells into mosquito eggs. When the eggs hatch they fly out your mouth, nose or possibly eyes, which kills you.
SCP-186 ("To End All Wars"). The weapons the soldiers were given did things like causing tumors to grow and forcing victims to stay alive even after half of their heads had been blown off.
SCP-212 ("The Improver"). This device performs bizarre surgical procedures on its victims that leave them worse for wear. Changes have included replacing teeth with sharp blades, replacing feet with pads, and replacing hands with tentacles or crab claws.
SCP-290 ("The Picasso Machine"). After a person enters SCP-290 it relocates their limbs and facial features to random parts of their body, but without affecting functionality. It also changes their internal organs, blood vessels and nerves to support the body parts' new locations.
SCP-412 ("Mutagenic Mirror"). Each time a subject views themselves in the mirror they suffer progressively worse bodily changes. The changes start out with enlarged lymph nodes, a facial rash, and skin discoloration. They eventually progress to an expanded ribcage, mouth cysts that force the jaw to stay open, and problems with the immune and reproductive systems.
SCP-420 ("Aggressive Skin Condition"). Anyone drinking SCP-420-1 (the liquid inside SCP-420) will suffer six stages of progressive body changes. The changes include finger nails, toenails and skin becoming brittle and growing at an increased rate, skin cancer, skin, hair and mouths growing in random locations, and the victim's skin killing and eating other creatures.
SCP-428 ("The Crowd"). All of the members of the crowd are former human beings who have had every part of their bodies other than their skin replaced with an unidentified material.
SCP-446 ("Human Mannequin"). SCP-446 was apparently originally a human woman who was changed into the form of a mannequin by unknown means.
SCP-466 ("Mobile Veins"). SCP-466 is the animated combination of the cardiovascular systems of four different people, plus the head of the original person. Originally it was the cardiovascular system of one person which somehow became independent of its original body. It obtained the additional three systems by attacking several doctors that were trying to help it after it appeared to die.
SCP-478 ("Tooth Fairies"). After SCP-478 infects a human victim's mouth, teeth will begin to grow at a tremendous rate. The growth will fill the victim's palate and then spread to the rest of the digestive tract, lungs and underneath the skin.
SCP-1707 ("New Skin"). Having your skin removed and replaced by a colony of worms can ruin your whole day.
SCP-1877 ("The Guts of the Earth"). The intestines of three people in widely separated areas somehow became connected. The connecting intestines actually physically pass through areas in the real world such as electrical conduits, telephone receivers, water mains, sewage pipes, and subway tunnels.
SCP-2051 ("Stromatolite Habitat"). Anyone who is completely immersed in SCP-2051 (a certain cove on the coast of Australia) will undergo a transformation the next time they enter a man-made body of water (bathtub, swimming pool, reservoir etc.). They will lose all external structures (nails, teeth, hair), their bones will dissolve and their internal organs will change to skin tissue. Their brain will be split up into nerve bundles throughout the body.
SCP-2102 ("Got Shoggoth?"). SCP-2102 is a human being who underwent an experiment. Whenever he suffers any kind of wound his body starts repairing itself at a rate a quadrillion times faster than normal. This creates large amounts of extra flesh, and he keeps on growing until his body is cauterized by flame.
SCP-2484 ("Parasitic Mayonnaise Worms"). If an amount of SCP-2484 exceeding 235 grams is removed from its container, it will attempt to enter the body of the nearest vertebrate animal, by force if necessary. If any vertebrate animal eats enough SCP-2484, the eggs in SCP-2484 will hatch and grow into worms that consume the victim's body.
SCP-2610 ("Procreation"). SCP-2610-E are altered human beings produced by genetic engineering and inbreeding. They have a variety of serious physical differences such as added or missing body parts (limbs, eyes, ears, etc.), collapsed rib cages, protruding stomachs and large growths.
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 Body HorrorFactory.
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.
Of a sort, in the Night Vale Presents podcast, Within the Wires. A hollow between the lower left rib and left hip of the Institute patient addressed by the narrator is supposedly occupied by a mechanical creature with "many legs". "Dozens" of legs, in fact, which sometimes poke around in her intestines. It also collects her memories.