Adventure Time. Notable in that the early parts of the show are more of the "wacky Surreal Humor" kind seen on most of the rest of this page, but later on, it drifts into the more philosophical style of mind screw, with more and more frequent dream sequences, metaphors and things like that. This goes hand in hand with it developing a complex plot.
"The World" takes the show's typical weirdness up to eleven, consisting of various skits which show that everything in the world (if not the universe) is sentient and talks.
"The Job" is about reality falling apart due to Richard getting a job, and is just as weird as it sounds.
"The Void" reveals that the universe is sentient, and has created a black-and-white dimension where it sucks in anything and anyone it considers a mistake, as well as sloppily erasing any evidence of their existence. This can include characters from other works of fiction (such as Clippy and the Crazy Frog mascot) and early drafts of the show.
The weirdest episode in the series so far is probably "The Countdown". Gumball and Darwin break the screen and the countdown that was on the screen, causing time to stop. They then make several attempts to restart time, causing a number of bizarre timelines including one where everyone is a quadruped, one where everyone looks like them, one where they're worshipped as gods, and one where everyone looks pissed off and yells everything they say in German. None of these are ever given any kind of explanation.
Avatar: The Last Airbender: Aang's stress-related hallucinations in Nightmares and Daydreams get so over the top that you might just forget that he's nervous about the invasion and start to think that the creators are on something.
Even though Ralph Bakshi's animated films are more known for their adult material, some of his films, especially Heavy Traffic and Coonskin, have trippy sequences that could be considered mind screw.
Courage the Cowardly Dog pretty much is this for all the episodes, but in particular is the weird nightmare sequence of the episode "Perfect" where there's a weird blue humanoid with a clothes clip for one arm and another arm connected to it's head. Word of God says it's a broken bugle from earlier in the episode, but most people call it a fetus or a "perfect trumpet thingy".
Drawn Together is a show where characters die and come back in the same episode with no explanation. It's set up as a show where cameras are watching them. Really think about how completely insane that is. Xandir claims to have died 4 million times to save his girlfriend...and he's gay. Everyone makes fun of Xandir for being gay even though Everyone Is Bi. They never care that Captain Hero has had sex with women, men, children, animals, dead bodies, robots, and family members. "A Very Special Drawn Together After School Special" is insane even by the standards of their show, as it features the characters doing roleplaying within roleplaying for Xandir to come out to his parents, which is completely pointless anyway.
Ed, Edd n Eddy: In "One + One = Ed", the titular trio try and know everything so they can become super-smart and famous. In their quest for knowledge, however, all of reality breaks down- trees are flat as cardboard, Eddy eats the sun, Nazz turns into a dinosaur, and on and on. The madness only ends when the Eds are flying on a balloon that gets popped by the animator's giant pencil. And they never speak of it again.
Eddy: (After three giant Kanker Sisters merge into a giant pair of lips) Ed, your story's getting weird.
The Futurama episode "The Sting", in which Leela's perception of reality becomes more and more deranged, with events that turn out to be dreams, a hallucination of a morbidly cheerful musical number, a 2001: A Space Odyssey parody, and descent into obsessive insanity. It turns out everything in the episode since the bee attack was her nightmare.
NC: I think my favorite episode is the one called “Future Tense,” where Goliath arrives in the future and all hell broke loose as Xanatos has apparently taken over. Trying to set things right, all the gargoyles get killed and slaughtered by Xanatos’ army. But then it turns out Xanatos is really a computer with all the memories of the original person. But THEN it turns out it wasn’t Xanatos at all; it was Lexington, who’s become overtaken by madness. BUT THEN it turns out it was all an illusion by Puck to try and get a mythical emblem from Goliath. AND THEN it turns out it may or may not have been a dream. AND THEN it turns out that Goliath is a woman! (A Photoshopped image of Goliath in drag appears with a dramatic music sting) Okay, that didn’t happen, but you get the idea.
Gravity Falls. The episode Dreamscaperers, particularly, as it takes place mostly within Stan's mind. Moreover, it introduces the character of Bill Cipher, dream demon who's been teased throughout the entire season, who's brought to the show with a demon summoning ritual. He also stops time, and after he vanishes everyone feels like they've been dreaming. He loves summoning terrifying things and joking about them nonsensically, and is implied to basically know most everything about the overarching mysteries of Gravity Falls.
The Society of the Blindeye's reveal calls into question the validity of everyone in the town's perception of events thus far.
The Grim Adventures of Billy & Mandy is more or less constructed from this trope. The various episodes follow vague premises with more Mind Screw moments and Big Lipped Alligator Moments than virtually any other show. A particularly memorable one though, is at the end of an episode where they unmask a villain (he's adult-sized) to reveal... an earthworm.
Among the Looney Tunes directors, Bob Clampett loved this sort of thing, often justifying it with All Just a Dream. He directed "The Great Piggy Bank Robbery" and "The Big Snooze".
In one Foghorn Leghorn short, he plays hide-and-seek with Egghead, taking a circuitous route to hide in a dumpster before proclaiming that Egghead will need a slide-rule to find him. True to form, Egghead busts out a slide-rule... only to dig a small hole nearby and pull a very confused Foghorn out of it. He returns to the dumpster but decides against opening, because "I just might be in there."
The Fats Waller cat in Clampett's Tin Pan Alley Cats lampshades things when he lands in a color retooling of the Wackyland scenes of Porky in Wackyland: "What's de mattah heah??!"
The 1968 short "Norman Normal" is a series of surreal vignettes depicting a day in the life of a nebbishy white-collar worker, depicted by him walking in and out of a series of doors. It starts with Norman's boss trying to pressure him into tricking a potential client into signing a contract by getting him drunk, during which Norman's boss and then Norman himself regress into children. Next, Norman has a conversation with his father, during which Norman's dad just rambles about When I Was Your Age..., floats around the room, then gives the vague advice of "Don't make waves" before literally fading into the wallpaper. The final sequence has Norman at a cocktail party, where one of Norman's friends Leo wears a lampshade on his headwhile saying "Approval" over and over again, he tunes out another friend who tries to tell a racist dirty joke, and he finally gets fed up and leaves the party when the barman calls him a lightweight. Then the cartoon zooms out to reveal the whole thing was literally happening inside Norman's head, through another door.
My Little Pony: Newborn Cuties: Over Two Rainbows is the insane story of Rainbow Dash (before she had a rainbow mane) spending ten minutes whining about her scarf while Sweetie Belle is born (wearing a nappy)... via the crossing of two rainbows. As all this happens the ponies' mouths never move once. "What is this?!" is the standard reaction of everybody that tries to watch it.
Discord in My Little Pony: Friendship Is Magic is fond of dulling out these. In his debut two-parter, he makes a glass to catch some of the chocolate milk he's making it rain, filling it from the top down, then proceeds to drink the glass, leaving the solidified chocolate milk behind. He then throws it over his shoulders, causing an off-screen explosion that makes the screen darker instead of lighter.
The episode "Monster from the Id" features the boys traveling inside the mindscape of their big sister in order to retrieve a lost memory, leading to them visiting various bizarre areas that represent Candace's neuroses and fears.
Invoked in the episode "The Remains of the Platypus", which opens with many purposely off-the-wall things going on, such as Perry powering Doof's latest -Inator while dressed like a butler, breakdancing British guards, Carl in a cage while wearing a squirrel costume, and people running screaming out of Phineas and Ferb's backyard from a bloated Major Monogram. The episode spends the rest of its runtime giving an explanation for all of the bizarre things going on.
ReBoot: The episode "Number 7" only makes sense when you realize it is a homage to The Prisoner. The end of the episode revealed it was All Just a Dream, but the Mind Screw elements make more sense because of that, and Matrix received some Character Development.
Regular Show has this built into its plot structure. Act I starts out with a fairly simple, straightforward, and every-day situation (learning to play guitar, getting tickets to a concert, throwing a friend a surprise birthday party, etc.), but by Act III, the characters' normal actions will usually have broken reality, woke up some kind of Eldritch Abomination, caused them to travel through time, or any other bizarre circumstance. And as soon as that dilemma is solved, the characters more-or-less brush it off in order to return their focus to whatever the mundane inciting incident was. Case in point: the pilot episode has Mordecai and Rigby play Rock–Paper–Scissors over a chair, them tying 100 times in a row ends up summoning a black hole, and once they solve that by intentionally breaking the tie, the duo starts playing the game again to decide who gets to drive the golf cart while cleaning up the aftermath.
The "Mr. Sparkle" commercial from "In Marge We Trust", where a Japanese detergent mascot that looks like Homer Simpson's head shatters a two-headed cow like glass (among other things).
Similar to the ReBoot example above, "The Computer Wore Menace Shoes" only makes sense if you know it's a parody of The Prisoner.
The Couch Gag from "Clown in the Dumps", created by none other than Don Hertzfeldt doing what he does best. It riffs on the show's Long Runner status by showing the Simpsons still on the air in the 106th century, where they're a bunch of gibberish-spouting mutants known as "The Sampsans".
A throwaway gag in a Season 18 episode has Homer casually implying that he was the real shooter of Mr. Burns in the infamous 2-parter, probably in reference to ongoing Epileptic Trees around the subject. Funnily enough, this was over a decade before a specific "Homer did it" theory blew up online to the degree that the creators had to debunk it.
The South Park episode "Grounded Vindaloop", going from Cartman to being in a virtual reality to the other characters being convinced they're the ones trapped in virtuality, a customer service man calling himself, and ending with the events taking place in real life.
In Spongebob Squarepants, the first episode where you see Pearl does not seem weird... Fridge Logic ensues, as you ask yourself, "How can a crab father a whale?!" And if you're thinking, "Well duh, she's adopted", Mr. Krabs has previously called Pearl "his own flesh and blood." And the show never elaborates.
"Squidward in Clarinetland". Trippiest. SpongeBob. Episode. Ever.
Many times during the show, they show people drinking and swimming in water, crying tears, and taking showers. While underwater.
The ending of "The Chaperone" confused a lot of viewers, making them wonder if it was SpongeBob who took Pearl to the dance or it was his supposedly inanimate decoy. It was the decoy.
The ending of "Back to the Past" with so many SpongeBobs and Patricks arriving from different timelines and universes; it's so strange that even Man Ray had to sit down to comprehend what the heck is going on.
At the end of the Super Mario World episode "The Yoshi Shuffle", Luigi's brain is apparently melted following this exchange:
Luigi: Uh, did I catch the ball? Mario: Whaddaya mean, catch the ball? You were the ball!
The final episode of Teen Titans (2003) was really more of a No Ending, but it was such an over-the-top and inexplicable No Ending that it has to be mentioned here. It has been stated in interviews that the show's staff wasn't too keen on explaining things in the story; what transpired here can be best described as that policy's logical conclusion. Though, the sort of question Glen Murakami wasn't keen on answering were things about the characters' non-suited lives, and the "how did villain X get out of the Cardboard Prison last time?" These sort of things he considered unimportant, a distraction from the main plot. This was the only episode in which nothing was made sense of. (Well, Beast Boy does move on after the Terra incident - which we'd thought him over three seasons ago. The rest is pure randomness.)
The episode of Totally Spies!, "Deja Cruise". To make a long story short, it was like the girls' dreams were having dreams. The WOOHP contract may as well have this clause on it: "CAUTION: Prolonged employment at this occupation may cause you to lose the ability to differentiate between fantasy and reality."
Transformers: Beast Machines was more of a Heavy Mind Petting, but it was still pretty clouded with symbolism, and the fact that it could be deciphered tended to raise another problem when the message didn't go over well.
Although it's a bit lighter than some of the other examples, the TRON: Uprising episode, "The Stranger". It mainly takes place in somewhere not-quite on the Grid, with a weird computer-like texture all over it, strange (for the show) colours, a villain constantly defying physics in an unsettling way even on the Grid, a bizarro doomsday device, and Beck nearly being boiled to death and seeing... Flynn-knows-what before he manages to break free. And to top it all off, it has an 'Or Is It?' ending.
In Ugly Americans, the entire episode of "G. I. Twayne" is practically a giant Mind Screw episode towards both the main character Mark Lily as well as the viewers. As it turns out the entire thing is just a pre-enactment. This screws Mark so much he shows clear paranoia at the end of the episode.
To summarize, the denizens of Hell hold a yearly "pre-enactment" of the End of Days — that year, however, it looks like a Batman Gambit where they'd use the pre-enactment to start the actual End of Days. Hilarity Ensues.
Uncle Grandpa is about a guy who is both the uncle and grandfather of everyone, and that's just the beginning of the weirdness.
Some Woody Woodpecker shorts can get very nonsensical, even by cartoon standards.
Brian: I am not following the story here. Stewie: Shut up.
Æon Flux. The TV show. Some episodes are worse than others, but the complete lack of continuity, bizarre dystopian setting, overtly philosophical conversations (or complete silence depending which season you're watching), and unusual symbolism that is indistinguishable from the Rule of Cool events. It's weird. It is, however, absolutely awesome. The fact that the creator Peter Chung seems to actually know what's going on, but deliberately stops himself when he starts explaining it is either very annoying or very liberating depending on how you look at it.
None of this is helped by the fact that each episode is a self-contained story that is clearly already in progress, with no recap and zero exposition. That or a Jungian nightmare, take your pick, either one is both valid and complete bullshit.
" is the standard reaction of everybody that tries to watch it.