Body horror is often accompanied by abject horror from a person at their own appearance, sometimes with a detailed inner monologue of how horrifying they find their own body.
You must abduct a mutated infant at some point, basically against your will. You're encouraged to kill it but can avoid this outcome if you try hard enough.
There are humans mutated to resemble animals (or animals merged with humans?) that you must fight. Retreating instead of fighting them is possible. There is currently one situation that requires you to doom an animal to a horrible fate in order to reach the good ending.
There is a mutated human-spider thing rendered in some detail that you encounter, they're friendly and have a big sidequest tied to them in the sewers.
Several bugs/bug-adjacent creatures appear in the game. The character Morton is a human mutated into a cricket, though he does not show his full form often.
The character Roaches is, as its name would suggest, a large group of roaches acting as one.
The character Philippe pretends to be a moth, but is actually a fungus.
The non-playable characters David and Antoine resemble a horrifying spider and dragonfly man respectively: the former is not hostile, the latter however is.
The true form of the character Lyle is a strange buglike creature with an extremely large face, however viewing it requires certain choices and he otherwise appears simply as a hooded man with a creepy face.
(SPOILERS SPOILERS SPOILERS) The worst offender is a parasite entering someone's pupil and them trying to pull it out, all rendered in pixel art. Don't complete the dripping pipe quest if this is a trigger for you.
The game generally isn't reliant on jumpscares but there are some. Towards the beginning of the game, an eye suddenly appears on a TV and loud audio plays.
There's an attack most characters can learn called vomit but it's not accompanied by any noises or visuals, and then there's a brief scene where the wall vomits up a disc after you feed it. I was personally safe with it as a severe emetophobe.
Someone has Vietnam-era war experience and PTSD related to it, exaggerated to an extreme degree by the eldritch phenomenon. There is also PTSD revolving around survivor's guilt, being a bad person, and intrusive thoughts that can occur if the protagonist looks in the mirror.
Flesh warps, plant matter warps, physical space and perception warp; the eldritch phenomenon in this game completely warps reality in a disturbing way.