History TookALevelInJerkass / WesternAnimation

* ''WesternAnimation/SpongeBobSquarePants'' was one of the most infamous cases of this between Season 6 and Season 9, until Stephen Hillenburg's return led to CharacterRerailment.
** Mr. Krabs, depending on the episode be it the first or the later seasons, varies from a decent, if money-obsessed, businessman, into a horrendous boss who has a MoneyFetish and ([[KarmaHoudiniWarranty almost]]) always [[KarmaHoudini gets away with his crimes]].

*** A post-HD example would be "Jolly Rodgers", in which both [=SpongeBob=] and Patrick seem to disrupt Squidward and follow him all over the hotel deliberately despite his insist to be alone, repeatedly forcing him to come to the jellyfishing convention with them, and they never stop until Squidward calls pest control and boots everyone out. In addition, they were the ones responsible for the urchin outbreak in the beginning.

* Talia undergoes this in the WesternAnimation/DCUniverseAnimatedOriginalMovies. In ''WesternAnimation/SonOfBatman'', Talia risked her life to save her son, Damian, literally taking a bullet for him. In her next appaearance, ''WesternAnimation/BatmanBadBlood'', she activly tries to kill Damian, and glibly tells Bruce, who she has brainwashed, that they can "make another."

** Lumpy Space Princess takes a level in seasons 5 and 6. In Season 5, she attempts to burn down the Candy Kingdom when she believes her boyfriend Johnny is [[MistakenForCheating cheating on her.]] In the Season 6 episode "Breezy", she [[QuestionableConsent makes Finn make out with her and she may or may not have forced him to take it a step further.]] Thankfully, "Elements" seems to bring her back to her regular (if selfish and spoiled) self.

* Princess Bubblegum of ''WesternAnimation/AdventureTime'' was given a few morally ambiguous traits in some of the earlier episodes. She sometimes let her anger get the better of her and would mercilessly pursue those who had wronged her. Some of her science experiments also went wrong, such as producing her extremely screwed up offspring Lemongrab. However, more often than not Bubblegum would show regret when she screwed things up, and work to fix her mistakes. Over the course of season 5, her actions turn from well meaning mistakes into outright atrocities, such as committing genocide on a group of defective robots, sacrificing one of her subjects because she thought he wasn't as valuable as Finn or Jake, throwing Tree Trunks' entire wedding into prison just because Tree Trunks preferred the fake King of Ooo preside over her wedding than her, causing almost the entire conflict of one episode just because she doesn't like people thinking of magic as anything than another kind of science, and in general showing no remorse for hurting people if she believes it's for the greater good. A canon video game also reveals that she trapped and performed painful experiments on the two Lemongrab brothers, when she had previously been shown trying to help them. The only reason she doesn't come across as a villain is because of the nature of these threats, namely evil!Lemongrab and that the fake king intended to make everyone his servants. She does [[TookALevelInKindness mellow out]] after Flame Princess gives a [[WhatTheHellHero serious]] [[TheReasonYouSuckSpeech piece]] of her mind.

* In ''WesternAnimation/{{Bionicle}} 2: Legends of Metru Nui'', Matau's just into the whole hero deal for sheer excitement, meanwhile Onewa seems to take every opportunity to belittle his companions, especially their leader Vakama. In the following movie, ''Web of Shadows'', Onewa's demoted to an even more minor extra, and Matau takes over his role of a {{Jerkass}}, putting such a stress on Vakama with his constant complaining that it leads him to do a FaceHeelTurn. Matau makes up for it in the end by realizing how mean he was and bringing Vakama back to their side.

** Even Kyle arguably got this. "Tonsil Trouble" has him laughing at his SitcomArchNemesis Cartman after he gets HIV, in "Douche and Turd" he almost has ''[[WithFriendsLikeThese Stan]] killed by Puff Daddy'' [[ItsAllAboutMe so he can get his vote for his candidate]] and then gets even madder at him for voting for Cartman's candidate, and "Fatbeard" shows him willing to send Cartman's entire pirate crew (including classmates such as [[ButtMonkey Butters]] and Clyde) to their death in Somalia.

*** Season 23 took this UpToEleven, where he stops caring about his family at all and accuses them of not caring about him if they express that they hate Tegridy Farms, and becomes a greedy, sociopathic monster who cares only about profits and commits numerous murders and unethical business actions to get more money. At this point, he's comparable to Cartman in terms of evil.

** WesternAnimation/DaffyDuck was introduced as a fun-loving nut, becoming more stable and ambitious by means of CharacterDevelopment, as well as more embittered and obnoxious in personality, often acting as an [[IneffectualSympatheticVillain antagonist]] to WesternAnimation/BugsBunny. His cruelty was taken to extremes with his pairings against 'WesternAnimation/SpeedyGonzales in [[DorkAge the DePatie-Freleng era]]. For instance, in ''WesternAnimation/WellWornDaffy'', Daffy is hellbent on keeping Speedy and a friend from a desperately needed well for no other reason than for pure maliciousness, and then attempts to destroy it for absolutely no reason except to be mean.
** One of the reasons ''WesternAnimation/TheLooneyTunesShow'' received [[BrokenBase mixed reviews]] was the fact pretty much ''everyone'' had their jerk levels geared up. And if seeing Bugs being rude was too much of a shock to fans, the fact that Daffy pretty much became a sociopath who sponged off Bugs and did anything short of torture towards his neighbors (especially Porky) made things worse for them, even if they scaled this down a bit during the second season.
* ''WesternAnimation/MickeyMouse2013'' makes WesternAnimation/DonaldDuck, normally a JerkWithAHeartOfGold, a straight-up {{Jerkass}}. The most infamous example is "[[Recap/MickeyMouseS2E19BroncoBusted Bronco Busted]]". The shorts in the later seasons,mostly the 2016 holiday special, Duck The Halls,managed to tone down his obnoxiousness and reverted Donald back to his usual JerkWithAHeartOfGold status.

*** In "Demolition Doofus", while he accidentally injures Mrs. Puff, he isn't less dickish since he proposes to call her "Mrs. Pop", says she looks better that way, and seems uncaring for her plight. Although Mrs. Puff is also uncharacteristically bitchy in the episode, going so far as to attempt to ''murder'' [=SpongeBob=], but that fails because of his bad driving and the fact he's an invertebrate. Oh, and she never gets arrested for it. [[{{Bowdlerise}} The book adaptation tones down her role a little]] to have her act slightly less jerky than she did in the episode,

*** In "Demolition Doofus", while he accidentally injures Mrs. Puff, he isn't less dickish since he proposes to call her "Mrs. Pop", says she looks better that way, and seems uncaring for her plight. Although Mrs. Puff is also uncharacteristically bitchy in the episode, going so far as to attempt to ''murder'' [=SpongeBob=], but that fails because of his bad driving and the fact he's an invertebrate.

*** There's the episode "Yours, Mine, and Mine", where Patrick "borrows" money from [=SpongeBob=] to "share" a Krabby Meal together. He of course eats the whole thing himself. Mr. Krabs then makes Sponge pay ''extra'' for the toy (which is really just a Krabby Patty that Krabs dressed up as a doll). Patrick then claims that since he and [=SpongeBob=] are still "sharing" that he gets to play with it. Long story short, Pat eventually never lets [=SpongeBob=] play with the "toy" (that he paid for) and he inevitably eats it just so [=SpongeBob=] can't have it. After Mr. Krabs punishes the two for fighting and the two eventually make-up, Pat offers to pay for some new toys, by using [=SpongeBob=]'s wallet. When [=SpongeBob=] calls him out on that, he asks him "[[KnowNothingKnowItAll Have you learned nothing about sharing?]]"

* Season 2 of ''WesternAnimation/IronMan'' saw its title hero adopt many of the less-admirable traits the comic Tony Stark had, as he decided to start keeping secrets and even faked his death without telling anyone about it, which caused Force Works to dissolve until the series finale. The "ComicBook/ArmorWars" adaptation had Tony commit many of the same actions he did in the comic version, including getting into fights with other heroes over the suspected use of his tech and shutting down the Vault.

** Squidward changed from a {{Deadpan Snark|er}}ing JerkWithAHeartOfGold who simply disliked [=SpongeBob=] and Patrick's childishness into a full-on {{Jerkass}} more openly hostile towards them, often without provocation.

** In the first season, Darwin was more carefree and cheerful, sometimes to a degree where he's more innocent but also more naive than Gumball. In the second season onwards, he's a lot more irritable, [[NotSoAboveItAll no better than Gumball in many situations]], gains the ability to commit random acts of violence and is more of a DeadpanSnarker. Even so, if he's still not the ''smartest'' in any given situation, however, he became more of a [[OnlySaneMan voice of reason]] in case something goes wrong, becoming more willing to call out Gumball's actins.

** If that wasn’t enough, Star's mother, Moon, took a much bigger one in Seasons 3-4, while in the first two seasons, Moon did start out as a [[JerkWithAHeartOfGold strict but honest]] parent who, despite her cold and serious nature and low tolerance for anything reckless and destructive, does care about Star and her husband, River at times (Also, some may consider that her strict attitude towards her daughter may have been a [[FreudianExcuse cause and a horrible effect]] on Star becoming more selfish and oblivious in S2b, since Moon has been so hard on Star her whole life before she sent her to Earth in the first episode,through she still loves her and wants the best of Star no less). But after her character development at the end of Season 2 and Battle of Mewni, her overbearingness and anger towards Star was taken to extremes and she goes from a serious,strict queen to an outright terrible and racist queen, who is often blinded by her hatred against monsters, gets mad at and acts more tyrannical towards Star more than usual after she returned to Mewni, and has a grudge against her grandmother Eclipsa for being in love with a monster and using dark magic on her. Despite having a [[FreudianExcuse reason]] for the way she is due to Toffee killing her mother, Comet, she ends up going down the wrong path to become such a horrible queen and bad mother to her own daughter by making the Magic High Commission lie to her family for years and has done a lot of bad choices in her life such as [[WhatAnIdiot leaving her kingdom to be taken over by Toffee by taking shelter at Buff Frog’s and caring more than her daughter’s safety than her kingdom]], [[NeverMyFault blamed]] Eclipsa for corrupting her arm due to the spell she performed with her harming it badly and called her evil not because of it,but for being in love with an Monster, and hastily attacked Meteora just as Eclipsa was succeeding in taking her down (which led to her isolating herself in the realm of magic and Meteora destroying her kingdom, leaving it in ruins). She was not even happy when Star told her to give her a fair trial much to her grudgement and resentfulness against Eclipsa and showed no care in Star trying to repair the monster-Mewman relationship (despite telling her earlier to seek a monster expert). Even through she did loosen up in Season 4 after Star rescued her from Pie Island after being transported there,she ended up becoming much worse at the end of the series when she teamed up with Mina Loveberry to remove Eclipsa from power after she became queen of Mewni as revenge for [[NeverMyFault making]] her lost in the magic realm and separating her from her daughter, Star. Her betrayal as well as lying to everyone and leaving millions of die in the hands of her Solarian warriors was the reason and cause for Star’s hatred and later destruction of magic in the finale. Moon's overall unethical, horrible actions, misguided judgements, and betrayal in the later seasons made her much worse to the point she ends up making Star look like a saint in comparison.

* Iron Man in ''WesternAnimation/{{Ultimate Spider-Man}}'' was initially a mentor to Spider-Man. However in "Swarm", he seemed much more disrespectful and distant towards Spidey.

** In season 4, between the stress of [[spoiler:becoming Queen]] and the breakup of the Best Friends Squad, Glimmer's negative traits start to take over. She becomes jealous and resentful of Adora, seeing her attempts to take the lead as challenges to Glimmer's authority [[spoiler:and blaming her for Angella's death]]. Her ruthless streak, hinted at in earlier episodes, comes to the forefront, and she starts taking bigger risks, using Adora as a decoy, lashing out at her allies, and so on. Even at her worst, though, she still keeps ''some'' positive traits; she seems genuinely friendly towards [[spoiler:post-HeelFaceTurn Scorpia]], for example.

** Throughout most of his Season Fifteen appearances for that matter, Mr. Mackey has started to reveal more and more darker personal issues, albeit ones he frequently vents out on the school's students. His hoarding problem led him to be violently protective of his belongings, while he and the school faculty became so obsessed with avoiding controversy over school deaths they decided to [[RefugeInAudacity kill Eric Cartman by]] [[ItMakesSenseInContext throwing him under a bus]].

* ''WesternAnimation/ThomasTheTankEngine'':

*** In the same special, The Fat Controller also feels like this. In fact, some fans thought he was actually going to tell Thomas he had had enough of him and intended to replace and sell him. Though to be fair, his attitude throughout the special stems from the fact that Thomas is causing tremendous amounts of damage both physically and financially [[RealityEnsues (meaning Sir Topham Hatt has to pay for repairs to the damaged coaches, listen to complaints from angry passengers, and deal with the repeated delays to the construction of the new branch line)]] and is refusing to take responsibility for his actions. Given that, it's [[JustifiedTrope understandable that Sir Topham Hatt seems stricter than usual.]] Then again, he was [[DisproportionateRetribution too harsh and unfair]] towards Thomas after the dynamite incident, not letting him explain that he was trying to save everyone and cruelly sent poor Thomas to his shed in disgrace.

* ''WesternAnimation/SpongeBobSquarePants'' was one of the most infamous cases of this between Season 5 and Season 9, until Stephen Hillenburg's return led to CharacterRerailment.

* ''WesternAnimation/HeyArnold'': While not all episodes had this trope affecting them, [[CloudCuckooLander Sid]] and [[CountryMouse Stinky]] often acted ruder and more troublesome towards a number of the other characters in some of the show's later episodes. In one case their heckling gets so relentless that ''Harold''[[note]]who had admittedly [[TookALevelInKindness done this tropes inverse]] by this point[[/note]] calls them out on it.

* In the original ''WesternAnimation/BobTheBuilder'' Series. Lofty (Bob's mobile crane) was a [[LovableCoward Lovable Coward]] who wouldn't hurt a fly . In the 2015 revival, he's a snarker who insults Scoop on a daily basis.