Insane Decay Of Mind: The Labyrinth Download PC...
Western Animation Superjail! is known for this, in particular the episodes "Dream Machine" (with Jailbot's dream of being the Warden's human(oid) son resulting in creepy animation part, and the part where the Warden dreams of his crotch morphing into Jared's head and face, while his dream version of Alice quickly rots into an angered zombie that shouts "I need my BEAUTY SLEEP!") and "Don't Be A Negaton" (the hallucination scene at the end, especially with the rotting dog and D.L. Diamond's actual face without his wig or makeup is exposed as sore-infested and decaying). [adult swim] shows in general could probably qualify.
Courage the Cowardly Dog tends towards this sort of style to keep its Defanged Horrors scary: on top of the creator's overall outlook (claiming heavy influence by Salvador Dali), the show often uses Medium Blending for when a villain really needs to stand out, like, say, the Spirit of the Harvest Moon, King Ramses, or that cute violin girl.
Avatar: The Last Airbender: In "Nightmares and Daydreams", most of Aang's nightmares (and later, hallucinations) are merely funny. However, his last nightmare before he decides to avoid sleep altogether (leading to the hallucinations) is downright terrifying, even making Momo (Aang's pet lemur) creepy.
Zuko's Nightmare Sequence in "The Earth King."
The paraphernalia wagon sequence from Halloween Is Grinch Night. It's very easily comparable to Yume Nikki, being basically the protagonist walking through a series of strange, nightmarish visuals.
On the topic of Dr. Seuss cartoons, The Butter Battle Book features a similarly creepy Disney Acid Sequence about building weapons of mass destruction. The Butter Battle Book is way darker than Seuss's other material for kids, and Ralph Bakshi directed the Animated Adaptation, so no surprise there.
The collective animation project Hopital Brut (French for "Gross Hospital") has something to do with horrific experiments at the eponymous hospital, including lobotomies that entail the complete obliteration of the rest of the head. It's best not viewed by the faint of heart or the sound of mind.
Adventure Time drifts into this sometimes: The episode "No One Can Hear You" features Finn waking up alone in a hospital, finding the Candy Kingdom abandoned except for a delirious and concussed Jake, who has convinced himself everyone is off preparing for a surprise party. Then Finn finds out everyone was abducted by a bipedal deer with human hands.
Marceline's father turns out to be a demon lord who rules over "the Nightosphere" which, as seen in "Return to the Nightosphere" and "Daddy's Little Monster", is more or less a cute, animated version of Bosch's hell.
The Powerpuff Girls exhibits this whenever Him (a crossdresser Humanoid Abomination) shows up.
Gravity Falls has Bill Cipher, living embodiment of all that is both hilariously deranged... and just plain deranged, when his interests are against yours.
Of all places, this shows up to surprisingly chilling effect in Thomas & Friends in "Rusty and the Boulder". It concerns a new quarry that's being dug in the mountains of Sodor, but the mountain they dig into happens to have a gigantic, unnaturally spherical boulder sitting on the cliff face high above, threatening to fall down at any moment. To make matters worse, the boulder is heavily implied to be sentient, with Rusty feeling like he's Being Watched whenever he's near it, and when rock fragments start falling onto the railway below, he observes "The boulder is telling us to go away." When it inevitably falls off the cliff onto the rail line, it seems to actively pursue the engines in ways that should not be physically possible and completely defy the laws of physics (moving absurdly fast, not losing any speed when going uphill, and even appearing behind Rusty and his driver at one point) before eventually destroying a shed and almost several of the engines. Oh, and it has a weirdly realistic face that we see twice, once when it's staring at Rusty on the clifftop and at the end when the Fat Controller moves it to another mountain very far away like he's trying to exorcise a demon.Fat Controller: (disturbed) We should have left this part of the island alone.
The Simpsons: Don Hertzfeldt directed this Couch Gag. Yes, it's a satire of a Franchise Zombie. Doesn't make it any less surreal/disturbing (it looks like something Starfish Aliens could make when trying to imitate The Simpsons; it even mentions viewers' flippers. And whoever made it is ruled by a self-styled "dark lord" who seems to want to remark that all animals can scream and that "amusement is control").
The show also parodied Twin Peaks in the second part of "Who Shot Mr. Burns?" Chief Wiggum falls asleep on the job and finds himself in a strange building (which looks just like the Black Lodge), where Lisa makes odd, cryptic references ("THIS... SUIT... BURNS... BETTER") in a stilted voice and reality changes at a moment's notice. The trouble is that Wiggum is too stupid to figure out what the heck is happening, and Dream!Lisa is eventually forced to drop the mysterious act and outright tell him her message ("LOOK AT BURNS'S SUIT! Yeesh!"). When the Chief awakens, he happily talks about the "weird backwards-talking dream" he just had, prompting concern from the other cops.
Some of the post-movie episodes of SpongeBob SquarePants qualify, possibly unintentionally. The most obvious case is the Season 7 episode "Squidward in Clarinetland": it starts with two nausea-inducing scenes of Krabs completely breaking out in hives, and SpongeBob getting the flesh of his right arm eaten off by a cloud of insect-like creatures... and then Squidward enters the safe. The poor guy first navigates a labyrinth of filing cabinets that could not possibly fit in there, while following SpongeBob, whose laugh is unusually creepy in this episode. Then he opens a door, and winds up in a field that is empty except for the giant clarinets growing out of the ground and a buried, talking eagle head, which eats him. In its stomach, we see that the eagle has multiple esophagi despite only having one beak. Then Squidward gets flushed out of the eagle's stomach, somehow winding up inside a pinball machine which turns out to be a giant SpongeBob, with a giant Patrick there to torment him as well. Even the Encyclopedia SpongeBobia admits that "this episode scares children." They would hardly be the only ones.
The Real Ghostbusters; especially episodes happening in Another Dimension or those that involve poltergeists, goblins and the like.
The Shivering Truth is essentially just a series of short nightmares directly transcribed into a television format, and in the creepiest possible stop-motion animation, with all the horrifying strangeness that implies. It's done by the same people who did The Heart, She Holler and Xavier: Renegade Angel, so if you've seen any of those shows, you know what you're getting into.
The OK K.O.! Let's Be Heroes episode "Plaza Alone" leans into this during its climax. After wandering the mysteriously empty plaza all day, KO, Rad, and Enid accidentally get locked in the bodega's break room. They then suddenly begin to hallucinate. Rad turns into a hot dog, Enid fails to stop KO from eating Rad and then explodes, KO turns into a horse, and they all panic about both their actual situation and their bizarre hallucinations.
Insane Decay of Mind: The Labyrinth Download PC...