The coma realm in general, a place filled with Grotesque Gallery residents, all of whom subliminally inject nightmares into the living in order to continue leaving and can potentially do a Grand Theft Me should the need arise to cause mischief while the real person is left imprisoned forever.
Julie's nightmare of Stu getting his life support literally cut off, as it's depicted with his sister (who is quite eager to do that despite how much she tries to hide it) using a huge pair of scissors to cut the tube that connects Stu to a large anesthesia bellows machine... which causes him to slowly deflate like a human balloon. Seeing a live-action actor being subjected to such cartoonish Body Horror just looks so wrong. Also counts as Tear Jerker since Stu is seeing all this from Hypnos' hideout and can only watch his beloved Julie having an awful dream, thus he destroys the viewing device making her at least wake up from it, at which point she cries over his comatose body.
As pictured, the Lynchian sequence where Stu ends up in one of his old paintings that involves a surgeon with an Eldritch Abomination coming out of his right eye trying to saw into Stu, who is a tiny humanoid root.
A lot of the inhabitants of Down Town. They really are the monsters of nightmares due to how eerily hyper-realistic and exaggerated they look.
Miss Kitty's heavily implications of eating the mouse guy.
The scenes where Stu is forced to take the body of a dead corpse and throwing his own organs at Monkeybone!Stu might be disturbing to some viewers.
