History CharacterDerailment / WesternAnimation

** Diesel 10, who currently provides the page image, is a very unique case of derailment. In his debut in ''WesternAnimation/ThomasAndTheMagicRailroad'', he was a [[KnightofCerebus murderous monster who was out for blood, wanting to completely and utterly destroy the steam engines]]. In his second appearance in ''WesternAnimation/CallingAllEngines'', he's somehow become [[TookALevelInKindness nicer]] with almost no given explanation, and quite willingly ''helps Thomas repair the new Sodor Airport''. In his defense, it was related more to necessity since a decline in tourists brought in by the airport in question would've spelt doom for the entire railway, including him. Even so, [[ThePollyanna he doesn't display any sort of gruffness or malice]], and again, does it with a big ''smile'' on his face. However, when brought in for the CGI series, he became more of a mix of the two. Whilst he certainly wasn't nice like he was in CAE, it wasn't up to his TATMR persona, as he's now become more of a WellIntentionedExtremist in that he wants his fellow diesels to receive more praise and attention than what they have, believing that they've become overlooked in favor of the steam engines, and while he certainly doesn't like them, he does realize when he's gone too far whenever he deals with them. It has given him more of a personality though, as some felt that his TATMR appearance was more of a GenericDoomsdayVillain than an actual character.

* ''WesternAnimation/AngelsFriends'': In season two, Urie suddenly wants to be the chief of the four girls ensemble like Raf do. Apart from the fact that AmbitionIsEvil for an angel, Urie never envied her best friend (or anyone else) in season one.

* ''WesternAnimation/AngelsFriends'': In season two, Urie suddenly wants to be the chief if the four girls ensemble like Raf do. Apart from the fact that AmbitionIsEvil for an angel, Urie never envied her best friend (or anyone else) in season one.

* WesternAnimation/MiraculousLadybug does this with one of it's more prominent characters, Chloe Bourgeois. While Chloe starts out antagonistic, throughout Seasons 2 and 3, she goes down a slow, but firm HeelFaceTurn throughout those seasons, only for that development to be sidelined in the Season 3 Finale, Resetting her back to her [[JerkAss Mean Girl]] Status she previously had. Following this in Season 4, any glimpse of hope she had was flattened, where she goes from being willing to commit a SelfSacrificeScheme during the episodes Zombizou and more recently Ladybug (where she shields her ExtremeDoormat friend Sabrina from a Scarlet Akuma.) But, not even half a season later and she has that same friend locked in a Closet doing her homework.

** Percy went from a mischievous CloudCuckooLander to a naive, forgetful moron who can't pronounce simple words, Toby was a kind and confident CoolOldGuy but later became a wimp with self-esteem issues, and Skarloey, previously one of the oldest and wisest engines on the island, is now childish and afraid of ''everything'' (from thunderstorms to the incline yards to ''the wharf''). Thomas himself was once depicted as friendly and helpful, [[SmallNameBigEgo if somewhat cocky and brash]]. He's now a poorly-written CreatorsPet that is obligated to make appearances in every single episode (even episodes about the narrow gauge engines) and dispense advice to everyone.

* Many of the characters in ''WesternAnimation/ThomasTheTankEngine'' have suffered from derailment... [[{{Pun}} thankfully not literally]].

** Ezekiel's case in TDWT is one of the most infamous in the show's history. Originally a meek and clueless homeschooler who got eliminated for [[InnocentlyInsensitive making several unintentionally sexist remarks]], he quickly became an EnsembleDarkhorse after Creator/TheKoboldNecromancer made him the main character of the ''Fanfic/TotalDramaComebackSeries'' and fleshed him out quite a bit. In response to fan demand to give him a second chance, the writers brought him back, but he was turned into a SmallNameBigEgo {{Determinator}} and an obnoxious {{Jerkass}} as some sort of CreatorBacklash to his unexpected popularity. After losing the first challenge for his team and being voted off, he decided to stow away in the ship's cargo hold, which eventually resulted in him mutating into a feral, barely-sapient [[Film/TheLordOfTheRings Gollum]] {{Expy}} with almost no trace of the naive and innocent farmboy he once was left in him.

*** Kyle also gets derailed in some "Kyle vs. Cartman" episodes. He's mostly somewhat [[DeadpanSnarker snarky]] but otherwise nice and definitely a positive character compared to Cartman, but some episodes have him be a [[{{Jerkass}} rude]] KnightTemplar who is [[NotSoDifferent as bad as Cartman]]. This characterization of Kyle is also used in other episodes, such as "Douche and Turd", where he uses Puff Daddy to [[WithFriendsLikeThese intimidate Stan]] into voting, and "Fatbeard", where he is willing to send Cartman's entire Pirate crew to their death in Somalia.

* Scott Summers/Cyclops on ''WesternAnimation/WolverineAndTheXMen''. In his origin episode Breakdown Cyclops, who has been depressed and ineffectual since losing his girlfriend Jean Grey, is revealed to have been extremely stupid and clumsy when he was first recruited to train as an X-Man. This apparently changed when Jean came into his life and "took the pain away" as Emma Frost, the rival love interest, put it. This is a big turn from the comics, where Cyclops was always a good, diligent X-Man, even as a student, where his primary problem was that he had weak social skills. This alternative characterization however embraces the stereotype that he is nothing without his long time girlfriend, while not showing anything suggesting he was ever a competent heroic leader.

** Seasons 16 and 17 were full of them. In "Flippity Francine" and "Francine Speaks Up" Francine is scared of attention despite loving attention and always wanting to be the star for the past 15 seasons. In "Read and Flumberghast" the entire third grade class is made way more gullible than ever. In "Opposites Distract" and "Prunella the Packrat" Arthur is a NeatFreak who throws everything he feels is old away, while in the older episodes he makes huge messes and is an extreme pack rat who won't even throw a popsicle stick away. The most extreme example is in "So Funny I Forgot to Laugh", where Arthur becomes a bully and Francine gets angry at him despite past episodes that revolve around bullying showing the bully (who is usually Francine) doing far worse things than what Arthur did.

** Duncan also qualifies because during his return in TDWT, he went from a carefree JerkWithAHeartOfGold who actually did have some degree of moral standards to a remorseless asshole with no redeeming qualities who would stoop to any level to be bad. Throughout the season, he holds the ConflictBall, cheats on Courtney with Gwen, never helps his team, cheats during the game, treats almost everyone like crap (especially Courtney), becomes a ManipulativeBastard, and helps [[BigBad Alejandro]] stir the pot for no good reason. It's no wonder he went from being one of the show's most beloved characters to one of its most controversial as a result of the season.

** Beezy in Season 1 was a JerkWithAHeartOfGold who was supportive of Jimmy, very mellow and easygoing, well-intentioned, and cared a lot about his girlfriend Saffi despite his stupidity and hedonism; the entire point of his character was that, underneath his many flaws and vices, he was a ''better'' person than his evil father Lucius. The Season 2 Beezy, on the other hand, is basically a big and fat version of Lucius with a gross case of SmallNameBigEgo and a total {{jerkass}} who treats everyone around him like garbage (to the point where the people of Miseryville hate him as much as they do [[ZeroPercentApprovalRating Lucius]]), including Jimmy and Saffi (whom he casually broke up with to chase after a GirlOfTheWeek).

* ''WesternAnimation/Ben10'''s DarkerAndEdgier sequel, ''WesternAnimation/Ben10AlienForce'', has Ben and Gwen exhibit different personalities than before, but that's excusable since it's been five years and they've matured. However, there is NO explanation for the change in Kevin, who not only has suffered massive BadassDecay, but is now a [[HeelFaceTurn good guy]] for poorly constructed reasons and shows [[SameCharacterButDifferent no signs of the sociopathic cruelty he did in the original series.]] Now all he can do is be blunt (especially about his [[StrangledByTheRedString crush on Gwen, which came out of nowhere.]]), demonstrate TheWorfEffect, drive them around in his beloved car, and occasionally thrive off of his reputation from back when he was an actual threat. Both ''Ultimate Alien'' AND ''Omniverse'' made attempts at CharacterRerailment, but the fanbase remains perpetually divided over how well either of them went.

** In the first three seasons, Sandy is a daredevil who is skilled in a variety of sports, including skiing, karate and weightlifting. Then in season 4 she suddenly became a scientist, and much of her characterization and humor started to revolve around her intellect and inventions.

** [=SpongeBob=] himself started out as a naive, yet kindhearted guy who cared about everyone no matter what, and had the innocence of a child. He later gets derailed into to an obnoxious, ManChild who pesters everyone he knows to play with him. He is often careless of others' safety, and cries and screams when his "friends" aren't around.

** In the WesternAnimation/WileECoyoteAndTheRoadRunner shorts in the [=DePatie=]-Freleng era (most notoriously by Rudy Larriva) the Road Runner actively fights back against Wile E. Coyote, something he rarely, if ever did in the original Chuck Jones shorts. This continues into 2003's "WesternAnimation/TheWhizzardOfOw" and the CG shorts from ''the Looney Tunes Show'',which kept the {{Slapstick}} nature of the franchise, unlike the show proper, such as "Silent but Deadly".

* While the fanbase seems completely divided whether WesternAnimation/DaffyDuck's {{Flanderization}} during the 1950s from a bombastic {{Cloudcuckoolander}} into a {{Jerkass}} SmallNameBigEgo counts as derailment or [[CharacterDevelopment development]], most agree it crossed the line during the Creator/DepatieFrelengEnterprises era shorts, where he was evolved into a humorless, FauxAffablyEvil villain for WesternAnimation/SpeedyGonzales. One could take it as a double-sided coin, as pitting Speedy against a more conniving villain did at least allow him to come off as more sympathetic and fallible more often than [[InvincibleHero he did against Sylvester]], though it still would have been a swifter transition with a more fittingly-callous character.

** Speaking of ''WesternAnimation/LooneyTunes'': Although WesternAnimation/BugsBunny's personality usually varied [[note]] Creator/FrizFreleng and Creator/ChuckJones made him an ingenious KarmicTrickster while Creator/BobClampett and Tex Avery made him a lovable [[ThePrankster prankster]][[/note]], most would agree he derailed in ''WesternAnimation/TheLooneyTunesShow'' where he evolved from a funny trickster to a [[TheGenericGuy bland and unfunny straight man]].

** In the WesternAnimation/WileECoyoteAndTheRoadRunner shorts in the [=DePatie=]-Freleng era (most notoriously by Rudy Larriva) the Road Runner actively fights back against Wile E. Coyote, something he rarely, if ever did in the original Chuck Jones shorts. This extends to ''the Looney Tunes Show'' (while the shorts keep the {{Slapstick}} nature of the franchise, unlike the show proper), such as "Silent but Deadly".

** In some of the CGI Roadrunner shorts on ''The Looney Tunes Show'' (while the shorts keep the {{Slapstick}} nature of the franchise, unlike the show proper), such as "Silent but Deadly", the Roadrunner actively fights back against Wile E. Coyote, something he rarely, if ever did in the original shorts.

** Speaking of WesternAnimation/LooneyTunes: Although WesternAnimation/BugsBunny's personality usually varied [[note]] Creator/FrizFreleng and Creator/ChuckJones made him an ingenious KarmicTrickster while Creator/BobClampett and Tex Avery made him a lovable [[ThePrankster prankster]][[/note]], most would agree he derailed in ''WesternAnimation/TheLooneyTunesShow'' where he evolved from a funny trickster to a [[TheGenericGuy bland and unfunny straight man]].

* While the fanbase seems completely divided whether WesternAnimation/DaffyDuck's {{Flanderization}} during the 1950s from a bombastic {{Cloudcuckoolander}} into a {{Jerkass}} SmallNameBigEgo counts as derailment or [[CharacterDevelopment development]], most agree it crossed the line during the De Patie Freleng era shorts, where he was evolved into a humorless, FauxAffablyEvil villain for WesternAnimation/SpeedyGonzales. One could take it as a double-sided coin, as pitting Speedy against a more conniving villain did at least allow him to come off as more sympathetic and fallible more often than [[InvincibleHero he did against Sylvester]], though it still would have been a swifter transition with a more fittingly-callous character.

*** Though, really, this change was happening even in some of the Looney Tunes shorts of the late-1950's and early-1960's. Witness Bugs's cartoons with Daffy Duck during that time period: he usually played the more sensible StraightMan to Daffy's hyper-idealistic [[StealthPun loonatic]] persona.

** Karen herself was always a BeleagueredAssistant, but was initially genuinely loyal and caring to Plankton despite her snarky qualities. Following the [[UnCanceled UnCancellation]], she has seemingly [[TheEeyore lost all sense of enthusiasm]] and openly vents her utter contempt for Plankton, placing him into high order HenpeckedHusband territory.
%%** Squidward was portrayed in the first seasons as a JerkWithAHeartOfGold who still likes [=SpongeBob=] despite his attitude, but he later started to hate him.

** In "Griffon the Brush Off", Pinkie Pie stops Rainbow Dash from pranking Fluttershy, saying she's so sensitive and even their most harmless pranks would hurt her feelings, and Rainbow agrees. Five seasons later in "28 Pranks Later", Rainbow pulls a prank on Fluttershy that is deliberately so frightening for her that she is tearing up and hyperventilating, to the point that she feels a need to call a meeting with all the Mane 6 to dicsuss this. This is also in contrast to Rainbow's compassion to Fluttershy in the Season 2 episode "Hurricane Fluttershy". Fans have argued that Rainbow might have thought Fluttershy was ready for pranks due to participating in a food fight in Season 2, but not only was this the last kind of prank that Fluttershy would find amusing, but Pinkie, in spite of what she said earlier, finds it funny.

** In "Griffon the Brush Off", Pinkie Pie stops Rainbow Dash from pranking Fluttershy, saying she's so sensitive and even their most harmless pranks would hurt her feelings, and Rainbow agrees. Five seasons later in "28 Pranks Later", Rainbow pulls a prank on Fluttershy that is deliberately so frightening for her that she is tearing up and hyperventilating, to the point that she feels a need to call a meeting with all the Mane 6 to dicsuss this. This is also in contrast to her compassion to Fluttershy in the Season 2 episode "Hurricane Fluttershy". Fans have argued that Rainbow might have thought Fluttershy was ready for pranks due to participating in a food fight in Season 2, but not only was this the last kind of prank that Fluttershy would find amusing, but Pinkie, in spite of what she said earlier, finds it funny.

** In "Griffon the Brush Off", Pinkie Pie stops Rainbow Dash from pranking Fluttershy, saying she's so sensitive and even their most harmless pranks would hurt her feelings, and Rainbow agrees. Five seasons later in "28 Pranks Later", Rainbow pulls a prank on Fluttershy that is deliberately so frightening for her that she is tearing up and hyperventilating, to the point that she feels a need to call a meeting with all the Mane 6 to dicsuss this. Fans have argued that Rainbow might have thought Fluttershy was ready for pranks due to participating in a food fight in Season 2, but not only was this the last kind of prank that Fluttershy would find amusing, but Pinkie, in spite of what she said earlier, finds it funny.