History Retcon / WesternAnimation

** Hexadecimal being infatuated with Bob. While she always had flirty relation with the Guardian, she never went was far as kissing him.

** Bob and finally kissed at the end of season 3, only to have them becoming JustFriends in the next season. All this so the ''My Two Bobs'' story arc could work.

** Hexadecimal being infatuated with Bob. While she also had flirty relation with the Guardian, she never went was far as kissing him.
** Game cubes having purple borders, while past seasons never shown such thing.

** Bob always having a wild ''No virus deletion'' policy and wanting to reprogram them instead.

** Game cubes having a purple border while past seasons never shown such thing, as they were limitless boundaries.

** Furthermore, in the third episode Avatar Kyoshi was not shown as the Avatar before Roku, in her place there was a male Earth Avatar. This was quickly fixed in the next episode.

** Kevin has his past added onto to make the complete overhaul of his powers and personality between the original series and AF/UA make at least ''more'' sense than it did originally. Also part alien; has the earlier energy powers ''and'' the new matter powers, but using energy makes him go nuts, making for the Kevin of the original series. Kevin was retconned further in ''WesternAnimation/Ben10Omniverse'', where it was revealed that he was not part alien at all, but the Ben 10-verse equivalent of a mutant.

* A season 3 episode (''Bart the Murderer'') establishes Fat Tony's name as William "Fat Tony" Williams. Several seasons later, he's canonically named Anthony "Fat Tony" D'Amico. It's either a case of this or [[SeriesContinuityError the writers forgetting they already named him.]]

** In the fourth episode, it is stated that Roger has been living with the Smiths for four years since Stan rescued him from the C.I.A., however in a much later episode there's a flashback of Stan giving him to Steve as a little boy for his birthday.

** Played straight with Francine's adopted sister Gwen. In the early episode "Big Trouble in Little Langley" she was established ([[TheUnseen via dialogue]]) as being a BrainlessBeauty who needed all the help she could get to survive, which was why her parents were leaving everything to Gwen in their will, trusting their 'smart daughter' Francine to be okay without their money. Years later in "Now and Gwen", when Gwen finally shows up on screen she does turn out to be beautiful, but of average or better intelligence and a hardened criminal.

* The ''WesternAnimation/JusticeLeague'' cartoons get rid of most of the annoying retcons in Franchise/TheDCU, but they make a few new ones. Doomsday showed up in the original ''Justice League'' episode "A Better World," in which he said he was an alien invader looking to see what Earth had to offer in the way of worthy opponents. He's never heard of Superman before and doesn't seem to care one way or another about him. Later on in ''Justice League Unlimited'' he was retconned to be a creation of Project Cadmus, who reverse-engineered him from Superman's DNA and conditioned him to hate Superman above all else. Then, to explain his appearance in the older episode, Cadmus shot him into space. His voice ven had modulation added to it.

* The ''WesternAnimation/JusticeLeague'' cartoons get rid of most of the annoying retcons in Franchise/TheDCU, but they make a few new ones. Doomsday showed up in the original ''Justice League'' episode "A Better World," in which he said he was an alien invader looking to see what Earth had to offer in the way of worthy opponents. He's never heard of Superman before and doesn't seem to care one way or another about him. Later on in ''Justice League Unlimited'' he was retconned to be a creation of Project Cadmus, who reverse-engineered him from Superman's DNA and conditioned him to hate Superman above all else. Then, to explain his appearance in the older episode, Cadmus shot him into space [[FridgeLogic for no good reason]]. He even got a completely different voice.

** The live-action SeriesFauxnale, ''Film/AFairlyOddMovieGrowUpTimmyTurner'', retcons the DistantFinale ending of season four TV movie ''Channel Chasers''.

** The season nine episode ''Let Sleeper Dogs Lie'' retcons Denzel Crocker's childhood as shown in season three's ''The Secret Origin of Denzel [=Crocker!=]'' The episode shows him to be complete jerk who lost his fairies due to turning 11, rather than being a nice kid who only lost Cosmo and Wanda due to Timmy interfering with his life and causing him to reveal the existence of his fairies. This also retcons the idea previously established in ''Channel Chasers'', where beyond revealing the existence of your fairies, the only reason you would lose them is if you either became an adult (which was Timmy's case) or your life has improved to the point where you no longer need them.

** The season nine episode ''Let Sleeper Dogs Lie'' retcons Denzel Crocker's childhood as shown in season three's ''The Secret Origin of
Denzel Crocker!'' The episode shows him to be complete jerk who lost his fairies due to turning 11, rather than being a nice kid who only lost Cosmo and Wanda due to Timmy interfering with his life and causing him to reveal the existence of his fairies. This also retcons the idea previously established in ''Channel Chasers'', where beyond revealing the existence of your fairies, the only reason you would lose them is if you either became an adult (which was Timmy's case) or your life has improved to the point where you no longer need them.

** In the original pilot, Vicky was apparently babysitting Timmy for the first time, and Timmy was ten. The first [[TheMovie movie]] reconned both points: Vicky had been Timmy's babysitter for a year, and Timmy was nine when he first got Cosmo and Wanda.
** The live-action SeriesFauxnale, ''Film/AFairlyOddMovieGrowUpTimmyTurner'', retcons the entire ending of ''Channel Chasers''.

** The Season 14 episode "201" retcons the twist ending of "Cartman's Mom Is Still a Dirty Slut", from way back at the beginning of Season 2 (twelve seasons before) by revealing that Liane was Cartman's mother all along and her claim of being a hermaphrodite was simply a cover-up to protect the identity of Cartman's real father, the former right tackle of the Denver Bronco. Said Denver Bronco turns out to be none other than Jack Tenorman, the man Cartman murdered and fed to his son Scott in the Season 5 episode "Scott Tenorman Must Die". Cartman seems more upset at the fact that he is Scott Tenorman's half-brother, thus making him half-ginger, than with the revelation that he killed his own father and then fed his remains to Scott. He feels better when Mitch Connor reminds him of the fact that he's also half-Denver Bronco.

* ''WesternAnimation/{{Fillmore}}'': episode 3 has Ingrid learn about Fillmore's delinquent past. Episode 8 establishes in flashback that he told her about it before even recruiting her to the Safety Patrol. It's unlikely Ingrid forgot, given that she literally has an eidetic memory.

* In a season two episode of ''WesternAnimation/AvatarTheLastAirbender'', Ozai and Iroh's father Azulon is said to have been Fire Lord for 23 years before Ozai and that Fire Lord Sozin ruled for the first 70 or so years of the 100 year war. The Nick website also provided a brief backstory for Sozin saying that he was a young man when he became Fire Lord shortly before Roku died and was prevented from starting the war until the elder Avatar Roku's death. Come season three where it's revealed that Sozin and Roku are actually the same age and that he was an old man when he started the war. In response, the creators revealed that Sozin ruled for only the first 20 years of the war before Azulon took over for the next 75 years before Ozai became the Fire Lord for the last 5 years. This has caused confusion for many fans.

*** Furthermore, in the third episode Avatar Kyoshi was not shown as the Avatar before Roku, in her place there was a male Earth Avatar. This was quickly fixed in the next episode.
*** On the show's website it suggests that Kyoshi was born on the island later named after her, yet we later find out that it wasn't even an island until she made it one.
* ''WesternAnimation/{{Futurama}}'', "The Why Of Fry". This fourth-season episode posits that the original accident causing Fry to be frozen and sent forward into the year 3000 was actually intentionally caused by Nibbler and the Nibblonians so that he could save the universe from the giant space brains. At first glance, this seems like a retcon; however, careful viewing of the original first episode shows the shadow of Nibbler underneath the desk as the accident happens and in a revisited scene his eye stalk poking out, proving that the [[TheProducerThinksOfEverything producers of the show set this up from the very beginning.]]

* ''WesternAnimation/TheSimpsons''
** The series has gone through a retcon as of the episode "That 90's Show." In the earlier episodes, Homer and Marge attended high school in the late 1970's got married three or four years after graduating from high school after Marge became pregnant with Bart, Bart was born in 1980, Lisa was born in 1982, and Maggie was born in 1989, but the series was retconned in the aforementioned episode. Marge in previous episodes had never gone to college, but was suddenly attending in the mid 90's; it led us to believe Homer had a Grunge band, whereas in an earlier episode he didn't understand grunge at all; and they also showed us that they dated for at least ten years before getting married and having the kids, who are now retconned into being born in the early 2000's.

* ''WesternAnimation/KingOfTheHill'': In "Death Picks Cotton", when Cotton tracks down Hank and company in a Japanese restaurant, it triggers his flashback, and he calls the Chef (who only speaks Spanish) a Tojo. However, part II of "Returning Japanese" had basically been about him forgiving the Japanese, and he was talked out of his scheme to spit in the Emperor of Japan's face by his illegitimate son Junichiro, resulting in apparent AesopAmnesia.
** For that matter, that episode {{Flanderiz|ation}}es him back into the JerkAss, verbally AbusiveParent he was at the beginning of the series, throwing out his CharacterDevelopment into a JerkWithAHeartOfGold.

* In the original ''WesternAnimation/TheFairlyOddParents'' pilot, Vicky was apparently babysitting Timmy for the first time, and Timmy was ten. The first [[TheMovie movie]] reconned both points: Vicky had been Timmy's babysitter for a year, and Timmy was nine when he first got Cosmo and Wanda.

** One of the biggest retcons was the episode "Where No Series Has Gone Before", where it is revealed that it is illegal to even mention Star Trek. Virtually every episode before that had at least one Star Trek reference. When Fry meets Leonard Nimoy at the Head Museum he calls him "Spock". When Fry is confused by the DOOP, Hermes says it's like the Federation on Star Trek.
*** In a DVD commentary, one of the writers suggested that charatcers were saying "Start Wreck" rather than Star Trek.

** It happened again in the FullyAbsorbedFinale for ''WesternAnimation/BatmanBeyond'', which threw together plot points from dozens of episodes ''and two movies'' into something they clearly weren't originally meant to be. It's cleverly pulled off, though, as any potentially created inconsistencies are rather smoothly {{Hand Wave}}d by a line from [[WordOfGod the creators]], stating that their choice to have [[spoiler:Bruce Wayne revealed as Terry and Matt's biological father]] was partly motivated by them realizing how [[spoiler:Terry and Matt having black hair is genetically improbable since Warren's hair was light-brown and Mary is a redhead]].

* ''WesternAnimation/ThomasTheTankEngine'': Reverend Awdry stated that the North Western Railway was built in 1914, mainly by Edward. In the 2009 movie ''Hero of The Rails'', it is stated that [[MerchandiseDriven the new character]] ''Hiro'' was responsible for building it. This may sound like a standard Ret Con, but keep in mind that Hiro is a JNR class D51, which wasn't built until 1936. And it doesn't help that Hiro is Japanese and thus runs on a completely different gauge than traditional British engines...

* ''Franchise/{{Ben10}}'':

** {{Lampshade|Hanging}}d in the 9th season episode "Excellence in Broadcasting": When the Griffins hear that Radio/RushLimbaugh is coming to town to promote his latest book, Chris recalls that, during Lois' brief stint at Creator/{{Fox News|Channel}} (in the "Foxy Lady" episode), she reported that both Limbaugh and Michael Moore were characters played by FredSavage. Lois [[{{Handwave}} dismisses]] this, explaining that even if something is true to begin with it becomes a lie when said on Fox News.