Characters undergoing Sanity Slippage in Fan Works.
Crossovers
- The ABC's of Fallout: Equestria
, a collection of short stories, has Irradiate, which tells the story of a mare who becomes a ghoul and slowly goes feral. - In Amazing Fantasy, years of constant defeats turned the already self-centered Mysterio into an individual obsessed with being seen as something more than the guy who Spider-Man beats, resulting in him committing much darker crimes on in both Izuku's and Peter's universes.
- This happens to some characters in The Infinite Loops due to the strain, frustration, and boredom of living through the same events many many times. Sakura is the poster child for this sort of thing, having gone off the deep end and lost all moral restraint due to having come to believe that nothing she does in the loops matters since the loop will just reset.
- Infinity Crisis:
- Daisy notes that the Red Skull must have gone insane after being trapped on that planet guarding the Soul Stone, but Steve simply observes that it would have been a very short trip.
- In Of Kryptonians and Queens, Merlin states that whatever dark arts Morgana used to extend her lifespan over centuries made her more dangerous and twisted than before.
- In Gamma Relations, Bruce immediately tells that Sterns' transformation into the Leader also drove him insane.
- Jaune Arc, Lord of Hunger (RWBY & Star Wars): Under the influence of the Mask of Nihilus and the Dark Side of the Force, Jaune Arc gradually grows more and more unhinged: depriving himself of sleep, becoming increasingly over-attached to the Mask, and growing belligerent, distant and volatile towards anyone outside his team.
- Aliens/Once Upon a Time fanfic Monsters: After the Marines' first encounter with the Xenomorphs, Killian quickly loses any hope for rescue and begins yelling at any setback that they are all dead
- In The Story to End All Stories, the villain has gradually descended into madness to the point that he is unrecognizable.
- Thousand Shinji: As the story progresses, the corrupting influence of the Chaos Gods upon Shinji, Asuka and Rei increases, and they became more psychotic and unstable. Shinji and Asuka become increasingly violent, the latter descending into berserker madness during two months Shinji was missing, killing criminals every night to lessen her pain and loss, and Rei turns their apartment into a garbage-filled shrine to decay.
- In Among Us in Character, Drama slowly loses it after she continuously fails to catch the killer, and dreams of her dead crewmates each night. It's later revealed this was the result of an alien parasite that infected her, which was slowly breaking her mind to take control of her. It succeeds.
- Calvin & Hobbes: The Series
- Calvin goes a little crazy trying to watch a pug in one episode.
- The final story has two separate plotlines: one concerning the return of Thunderstorm and another concerning the Slender Man showing up. When the plots intersect, Thunderstorm starts displaying signs of this.
- Jack in Part 1 of Cave Story vs. I.M. Meen and for good reason. After being trapped inside an insane pedophile's sick mockery of a yuri pairing fanfic between his girlfriend and his girlfriend's best friend, being forced to work a part-time shift at a restaurant called Diarrhea Bell, being forced to watch the two girls 2-Girls-1-Cup each other right in front of his eyes, and being tickle-tortured and thrown in jail, Jack lets loose with this underrated gem of a scene, cementing this story's status as one of the secretly best fanfictions of all time:"I am Jack. Woe is me for I am wrongfully imprisoned. I am Jack! Sad and unhappy am I without friends. BOO HOO!! BOO HOO HOO HOO!!! (blows snot into handkerchief and smears it all over the floor)"
"Emptiness wells up in my tortured soul. I'm going to...GOING TO...(vomits all over the floor)"
"I am Sue; I also am indeed BLEAUGH! (dumps mixture of random condiments and gross stuff on the floor)"
"I'm just Toroko but I'm gonna barf too, and the MUSTARD, MUSTARD BARF MUSTARD BARF!!! (dumps ketchup and mustard all over the floor)"
"(soaks hands with the combined mixture) BEHOLD the GOOEY SLOP of our SORROW! (smears it all over his face) IT IS...SLOBBER...DAMMERÜNG! THE TWILIGHT OF THE CONDIMENTS!!! (removes hands from face and screams to the heavens, palms facing skyward) WEEP FOR THEM, WEEP FOR THEIR SORROW-HO-HOHO-HOHH!!!"
"Yes, Jack, my delicate psyche has come horribly unglued!"
- Code Geass Megiddo: Suzaku has been on a gradual descent to insanity after he murdered his father to save Lelouch and Nunnally's lives, but after Euphemia's death and the events that transpired as a result of that (including learning that his best friend was his Arch-Enemy), that descent accelerated and never stopped. By the time the narrative truly starts, Suzaku's Mask of Sanity is barely holding on and begins to crack when Lelouch is kidnapped by the Black Knights, cementing his inevitable return as Zero, and full-on breaks when they finally confront each other at Pearl Harbor. At this point, several other characters have become aware of how insane Suzaku truly is, and believe that if Lelouch still cares for Suzaku, on any level, killing him would be merciful.
- Kara of Rokyn: According to Nasthalthia's story, her uncle Lex Luthor used to be a hopeful, awkward, brilliant kid before running into Superboy. Lex initially befriended Superboy, but then he started blaming him for everything that went wrong in his life. At the beginning Lex merely wanted to show Superboy off, but as his obsession grew Lex gradually became madder, more irrational and more twisted, and quite soon he was plotting ways to murder his ex-buddy. When the proper story begins, Luthor has lost any redeeming qualities and is nothing but a ruthless, cold psychopath overwhelmed by inexhaustible hatred.
- Supergirl (2015) fanfic my youth is yours: Flashbacks show how Lex went from Lena's cool big brother who was very supportive of her relationship with Kara to a violent human-supremacist willing to do anything to take down Superman.
- Return to Krocodile Isle: A decade of isolation in his Krew's basement has left K. Rool not entirely there, with his game signature Mad Eye and occasional static representing his newly explosive temper boiling to the surface.
- Dear Journal: I'm Crazy: As a result of Doug running out of medication, the things he saw, from his peers' abnormal skin tones to Skeeter's honking, slowly come back to haunt him. It all comes to a massive Freak Out weeks later, leading to Doug being committed to a psych ward.
- In Dragon Ball Z Abridged, Piccolo and Vegeta suffer this when they spend time in the Hyperbolic Time Chamber by themselves. Piccolo starts hallucinating Cell after spending some time in there and decides that's enough training. Vegeta's the strange one as he resorts to a broomstick and a volleyball made up to look like Nappa after three days. In real time. Mr. Popo changed the time dilation in there, most likely in revenge.
- Springtrap and Deliah: In the Dark Ending, Springtrap cracks and falls back on his murderous ways from the fear of losing Deliah.
- Fireside Tale: Anna grieved over Elsa for the rest of her life. She was considered "mad". Even when Arendelle became uninhabitable and everyone else left, Anna stayed.
- Kingdom of Isolation: Anna's brutal death takes a toll on Elsa. She shuts herself from everyone and creates a "perfect world" of snow people where Anna is alive and it's her coronation every day. Her parents and Anna are all alive while Hans is a pile of slush in the prison. In the real world, Arendelle is in turmoil because there's a raging blizzard.
- Abraxas (Hrodvitnon): Some of the Titans — not least the alien and telepathic Ghidorah — have Brown Note effects on humans when they try to communicate, which can cause severe sanity erosion if it gets serious enough.
- After several months, the lingering telepathy in Ghidorah's decapitated head has caused Alan Jonah and some of his paramilitary whom have been spending time around the head to lose their minds: becoming increasingly withdrawn, depriving themselves of sleep, and believing that they can hear the head talking to them. Jonah experiences a personality shift and becomes eerily enthralled by the head in an almost religious manner, while one of his subordinates has a different reaction, clawing bleeding furrows into his temples with his fingernails and becoming suicidal.
- According to Word of God, the Dyatlov Pass incident in this universe was actually caused by a hibernating Titan's bio-acoustic sleep-talking driving the Soviet hikers insane.
- The Death Eaters' Disney World Trip: The entire titular trip is described to be one to the Death Eaters, and to Snape in particular due to his status as the Only Sane Man. Chapter 7 is even titled "Dwindling Sanity" by the author.
- Starting from about one-fourth into The Very Secret Diary, Ginny begins blacking out, sleepwalking, and behaving unusually enough that her family starts to worry. This is thanks to Tom Riddle possessing her without her knowledge. Ginny, not realizing Tom's responsible, confides in him, making it that much easier for him to Gaslight her and make her question her own sanity. Once she finally realizes what's really going on, things get worse. Much, much worse.
- Austria/Roderich Edelstein in the 1983: Doomsday Stories is portrayed for the most part as undergoing through this. His obsession in finding out whether Hungary survived Doomsday grows increasingly desperate (and irrepressible) over time to the point that others eventually start wondering if he's gone delusional from grief. He doesn't. It's also mentioned to have happened as well with Romano (hijacked by The Mafia as his brother's successor) and Poland (having his personality shattered).
- Gaz, Taster of PTSD: Due to not being able to sleep due to her trauma nightmares of the pork-tasting incident, Gaz slowly starts going crazy. The nightmares get worse, she starts psychosomatically tasting pork again despite the curse not being active, and her personality overall starts fraying. This eventually leads to her exploding on Torque when he mocks her with a pig's head, and she spends some time in a mental hospital before she finally starts getting better with Dib's help.
- Queen of All Oni: Her encounter with Lung leaves Jade with some severe PTSD, which only worsens as time goes on. It finally culminates with her confrontation with Tohru in the Vault of Endless Night, which convinces her the heroes are all out to kill or seal her, at which point she snaps completely.
- Satsuki undergoes this in chapter 5 of Come find me, again., due to depression over the loss of her sister. After noticing some changes, her parents make her come stay with them (or she'll be put in the hospital) and, when she's brought home, she gets worse, as she starts hallucinating, dancing on the widow's walk railing (almost falling off), and even broken glass (without shoes). Afterwards, she's hospitalized, where she starts to improve.
- Book 5: Legends: Temuji’s plan in the final chapters seems half-thought out at best, and gets worse the longer they go without fulfilling it, culminating in a Villainous Breakdown worthy of Azula's.
- FIRE! (DarkMark): Firebrand was never the most stable villain, but he endeavoured to be a cold, cunning schemer. When his father dies, though, Firebrand completely loses any semblance of sanity and develops a "Kill them all" mindset.
- Jack O'Lantern, the Arch-Enemy of Ultimate Spider-Woman, commits increasingly violent and destructive crimes as the series progresses. He goes from robbing banks to taking people hostage to going on killing sprees to orchestrating a bloody city-wide Mob War. Even in jail, we see him fantasizing about carving up human heads the way people do Halloween pumpkins. What's unusual is that Jack always had these sadistic urges-the Sanity Slippage comes from the escalating nature of his crimes.
- Miranda Lawson undergoes this in It Got Loose and Killed All Our Guys: The Project Lazarus Story, brought on by a mixture of being asked to bring someone back from the dead, the Illusive Man randomly asking for her to add modifications to Shepardnote , dealing with her (rapidly dying) co-workers, and the sheer isolation. She eventually declares Dead Shepard her best, and only, friend, and feels betrayed when he comes back to life.
- Le Papillon Rising takes Adrien Agreste and slowly twists him into a psychotic, obsessive, slightly sociopathic Yandere through use of the Butterfly Miraculous. It's worth noting that this is an AU where Adrien is the main villain.
- Lila Rossi: Queen of Lycée: Lila's obsession with being popular works against her when she becomes obsessed with beating Juleka for Prom Queen, and gets seen as crazy for wanting to win against a girl who lost her leg in a car crash. Her fall from grace when she gets exposed as a liar and blackmailer only makes her far worse. In the last two chapters, this ultimately leads her to murdering everyone that had a part in exposing her, with Juleka barely surviving by naming Lila as Prom Queen, with the Ax-Crazy girl celebrating her victory even as she is arrested by the police. The story ultimately ends with Lila in a mental institution, proclaiming that she is the queen of lycée over and over again.
- Cain: After witnessing All Might telling Izuku that he can become a hero, Katsuki becomes increasingly obsessed with ensuring that never happens. So far as he's concerned, the only one worthy of being mentored by All Might is HIM. Thanks to the preferential treatment and ego-stroking he's received at Aldera, Katsuki struggles with the concept of not getting his way, failing to see how his various attempts at sabotage are destroying any chance he had of impressing All Might. He only spirals further out of control once Izuku transfers out of Aldera, culminating in him triumphantly declaring "This is the story of how I became a hero" while he tries to suffocate Izuku with a Vorpal Pillow.
My Little Pony: Friendship Is Magic
- In the vein of the Cutie Mark Failure Insanity Syndrome described in the Western Animation section, The Audience by Reality Check states that Trixie herself is diving into one as her special talent isn't magic like most unicorns, but rather stage magic, illusions and theatrical personalities. The constant heckling, jeers and challenges towards her achievements that she was receiving were making her the Jerkass that she was portrayed as in canon.
- In Ave Sonata, this is apparently why Sonata Dusk is The Ditz.
- Twilight and Pinkie Pie go though this in Bride of Discord, after Discord takes Fluttershy away, due to both losing a friend and in Twilight's case, working herself to the bone and refusing to rest, while trying to find any possible way of getting her back.
- Platinum from A Brief History of Equestria suffered from this during the Winter War due to her plans for Unicornia falling apart. Clover had to lock her up in her chambers for her own good and take over the war effort. She broke out in time for the events leading to the Warming, and recovered after the Windigos were defeated.
- Nav starts showing signs of this in Diaries of a Madman, as he becomes far more reckless and depraved over the course of the story.
- Loved and Lost: Prince Jewelius was hardly ever sane to begin with, but after Princess Luna thwarts his attempt to hang Celestia, he gradually undoes all the hard work of his manipulations by losing his composure, responding angrily to subsequent setbacks in his plans, putting forth less effort into restraining his Berserk Button regarding the adoration directed towards Celestia and Cadance, and reacting petulantly to dissension/disagreements from others.
- Memories has Serenity. When we first see her, she's like Pinkie Pie, a happy, cheerful, harmless, fun-loving, chaotic, Cloudcuckoolander of a prankster with a soft spot for Discord. Then she dies and comes back to life. Cut to the epilogue and sequel and she's giving out Slasher Smiles, maniacal laughter, telling Discord that she wants to overthrow his mother and rule in her place, and finally saying that together they'll kill Celestia.
- The Rise of Darth Vulcan: The Alicorn Amulet should be doing this to Ted/Darth Vulcan, and the fact that it doesn't appear to be is worrisome for the heroes. Comments by Word of God, and in-universe by the Princesses regarding Ted's "True Self" being appalled at his actions, suggest that he was suffering from this even before he put on the Amulet, from years of convincingly pretending to be a cruel bully in order to avoid bullying himself. As such, the Amulet can't drive him insane, because he was never quite sane to begin with.
- Rocket To Insanity is a fanfic where Cupcakes (Sergeant Sprinkles) is a recurring nightmare of Rainbow Dash's. It gets to the point where Rainbow Dash withdraws from her life and distances herself from everyone else. When Pinkie Pie tries to cheer up Rainbow with a cupcake, Rainbow snaps and kills Pinkie in what-she-thinks is self-defense.
- Estee's Triptych Continuum has one in Permanent Record, wherein a poor guard is driven to utter and absolute madness over time by the antics of the Cutie Mark Crusaders, eventually culminating in their utter certainty that everything which goes wrong is their fault. To be fair, though... usually it is.
- Spike goes through one throughout Zenith, which stems from his Undying Loyalty to Twilight.
- A Crown of Stars: Jinnai, this story's Big Bad, became much more paranoid (and a big time megalomaniac) since he overthrew former Big Bad Winthrop because he realizes that the same thing could happen again; only this time with his head on the chopping block.
- Viva La Vida: Olive gradually starts to slip in both alliance and mental health over the course of the story, with her conflicting emotions causing her to lash out at those around her. And with her only attempt at reaching out to someone for help going horribly wrong, she eventually completes her Face–Heel Turn and goes to the odd side in full (in the Bad Ending, at least). Chapter 4 even implies that Olive is completely unaware of her thoughts or actions when it comes to viewing Odd Todd as an ally rather than as an enemy.
- This Bites!: During the Enies Lobby arc, Sengoku combines this with Unstoppable Rage. Every piece of bad news that comes his way drives him closer and closer to the edge, and by the time he's finally on his way to the Judicial Island himself, he's basically in full-out Villainous Breakdown mode.
- Reaper was already Ax-Crazy in canon. In Break My Heart, Break Your Heart, he gets worse. Way, way worse.
- Team Rocket Roots: After her favorite agent, Miya, went mysteriously missing while on a mission, Team Rocket's Madame Boss Gianna began slipping.
- the ringing in my ears gets violent employs this throughout Leon's Apocalyptic Log, depicting his deteriorating mental state and growing Loss of Identity in true Resident Evil style. By the time Chris finds his last note, it's barely sensible enough to be read. A later section from Leon's POV depicts how broken and erratic his mental state is, by the time of the story.
- Coeur Al'Aran:
- Arc Corp: The citizens of Mountain Glenn, after twenty years of being trapped in a time loop-esque anomaly which causes them to constantly reset, have gone completely insane and homicidal.
- The Eternal Crown: Salem has taken over the world because centuries ago, she found a way to permanently disable Ozma as her adversary: she tortured him and broke his mind so thoroughly that the insanity carries over to any new host he possesses after his previous death, rendering him incapable of opposing Salem before her agents track down any host exhibiting the telltale signs and off them. Although Ozma's soul is showing signs of slight mental recovery in the show's present when he possesses Jaune.
- Knight of Salem: Getting unofficial "training" lessons from Tyrian of all people, which include randomly ambushing them, are enough to turn Team RWBY into unmatched fighting machines, at the expense of them turning their own dorm into a death-trap for any unauthorized intruders and also combing everywhere they set foot outside of the dorm for any sign of another ambush by Tyrian.
- Null: Jaune's mental state takes a few major hits, on account of being betrayed, cut off from his only other allies and left for dead by Blake when he's a wanted fugitive on the run from a powerful conspiracy, and on account of Team RWBY's intervention and lack of awareness getting his mother killed while he could only watch.
- Professor Arc II: Headmaster: By the time Cinder escapes her imprisonment, she's convinced that literally everything is part of Jaune's plan to take over the world, to the point where she rants at the sky, and she kills her own rescuer and waits to be recaptured by the heroes just to show that she's done playing Jaune's perceived games.
- Relic Of The Future: Lionheart has naturally been good at hiding it for years, but in his last couple scenes before his death, it's clear that his mind went right out the window the day that the Relic of Knowledge told him and Raven that Salem can't be killed by them, when he misconstrued that as meaning Salem is truly unbeatable and never will be beaten, years ago.
- The Raven's Plan:
- Stannis' time in the Black Cells has clearly damaged his psyche. By the time Robert and Renly visit him, he's seething in rage at the very sight of them, demanding to understand why it is that he's always been The Unfavorite out of the three of them and wondering what Renly could have possibly done to earn Brienne's Undying Loyalty, and when he learns about Jon Snow's true identity, he starts laughing at them before proclaiming himself to the "one true king of Westeros, Jon Targaryen".
- Lysa was hardly the picture of good mental health before the Remembering, but after? She's madder than the Mad King and a threat to herself as much as she is to everyone else. It's so bad that Yohn Royce currently has her drugged to the gills with milk of poppy for everyone's sake.
- Much like Lysa, Cersei wasn't all there to begin with, but after she's thrown into the Black Cells she starts losing her mind. Not helping the matter is Robert, who is deliberately tormenting her as payback for their toxic marriage.
- Afterglow: At the end of the game, Walker was... not quite right, to put it lightly. He does not get better as indicted by the fact he's hallucinating a dead Lugo and Adams alongside sporting a Beard of Sorrow:
- Total Drama Stranded: Briony gets a major one very quickly when Calvin begins relentlessly bullying her.
- From the sister story, Total Drama Switcheroo, Missy gets an even bigger one.
- Transformers Animated: Cybertronian Genesis: One of the main focuses of the narrative for both the original story and its sequel is Megatron's slow descent into madness as his obsession with defeating Optimus Prime grows. Eventually, it becomes so bad that Starscream calls him out on it. He only manages to snap out of it when Gigatron gets involved.
- In Turning Red: Secrets of the Panda, Jason Vaugn loses all of his sanity during the confrontation at the CN Tower, leading to him trying to attack Mei and Xia in a blind fury.
- In Being Dead Ain't Easy, Seto Kaiba slowly loses his mind as the story progresses for a variety of reasons, including guilt over Joey's death, obsessively trying to find a way to save Joey, lack of adequate food and sleep, KaibaCorp not doing well, worry for his own life and Mokuba's, and synchronization with the dying Joey.
