History WalkingSpoiler / WesternAnimation

** The entire Changeling species undergoing a HeelRaceTurn in the Season 6 finale, physically changing their appearance in the process. Thorax is a natural extension of this, as he's the TokenHeroicOrc who helped caused the change to begin with.

* It's hard to talk about the Blue Spirit in ''WesternAnimation/AvatarTheLastAirbender'' without spoiling that he's really the SecretIdentity of Prince Zuko.

* ''WesternAnimation/HazbinHotel'': Vaggie is Charlie's devoted girlfriend, but to discuss her character to any real degree beyond that role means delving into the reveal that she's really a FallenAngel and a former high-ranking member of the executioner squad.

** Simon Petrikov, aka the Ice King, is an interesting case of this, as the character has been in the show since Day One. However, nothing can really be discussed about him without mentioning the season three and four plot twists that completely turn the character and the show's universe on their heads: he's over a thousand years old, having lived as a antiquarian prior to [[WorldWarIII The Mushroom War]], and flashbacks to this era have him referencing real world locations and pop culture. He was the foster parent of Marceline until her early teens, and the magic crown he wore in order to protect himself and her was what [[WithGreatPowerComesGreatInsanity drove him to utter madness]] and made him unable to remember his life as Simon. Prior to "Holly Jolly Secrets" and "I Remember You", which revealed some of this information, Ice King was played more as a pure joke villain rather than a sympathetic character, Ooo's status as a post-apocalyptic Earth was just WordOfGod trivia instead of something important to the show's developing MythArc, and Marceline's own past was similarly shrouded in mystery. Talking about Simon Petrikov is necessary to explain an important part of the show's lore and why both Marceline and Ice King's behave the way they do.
** Betty Grof, Simon's fiancée. Simon believed she was so scared by his behavior when he first put on the crown that she abandoned him, and ultimately died during the Mushroom War. You can leave at that, but you'd be loathe not to mention that her appearance was actually her entering a time portal to be with Simon in present-day Ooo. All her future appearances and characterization from the episode "Betty" onward revolve around her attempts to reverse the effects of the crown or prevent the Mushroom War from occurring in the first place.

** The big reveal of Book 1 is that "the Conductor" is actually a [[TheUsurper usurper]] named Amelia, motivated by the death of [[TheLostLenore her fiancé, Aldrick]]. It's very hard to talk about either of them without revealing that.
** In Book 4, Kez repeatedly mentions about her roommate, Morgan, showing a picture of a man posing outside of a castle. In the ninth episode. we learn that Morgan is ''[[SapientHouse the castle]],'' and that the man is Jeremy, who left the Train after getting over his mother and sister's deaths.

* ''WesternAnimation/TheVentureBrothers'' has the Blue Morpho. He's not brought up by name at all until season 6, when the Monarch discovers his lair underneath his condemned family home, but his existence puts ''a lot'' of the show's historical events in a different light. Not only is he the Monarch's father, he was a member of the original Team Venture who Jonas Venture constantly mistreated, up to and including having him salvaged from the plane crash that killed his wife and [[WeCanRebuildHim making him into a helper robot for the Ventures as "Venturion"]]. And if ''that'' wasn't enough, despite Kano putting Venturion out of commission for nearly killing a young Rusty, he was later salvaged ''again'' by Dr. Z, becoming the villain and eventual Guild councilman Vendata, who [[AmbiguousSituation may have been]] the one to ultimately have Jonas ThrownOutTheAirlock of Gargantua-1.

** Twilight Sparkle, aka ''the show's main character''. There's no getting around the fact that she became a [[RoyalsWhoActuallyDoSomething princess]] at the end of the third season. Her new [[WingedUnicorn wings]] are a dead giveaway

** Twilight Sparkle, aka ''the show's main character''. There's no getting around the fact that she became a [[RoyalsWhoActuallyDoSomething princess]] at the end of the third season. Her new [[WingedUnicorn wings]] are dead giveaways. Nor the fact that she becomes the sole ruler of Equestria in the series finale.

** Twilight Sparkle, aka ''the show's main character''. There's no getting around the fact that she became a [[RoyalsWhoActuallyDoSomething princess]] at the end of the third season. Her new [[WingedUnicorn wings]] are dead giveaways.

** Discussing Starlight Glimmer. Talking about the character after Season 5 is impossible without revealing that she pulled a HeelFaceTurn at the end of it and became the [[SixthRanger seventh ranger]] to the Mane Six.

* ''WesternAnimation/RiseOfTheTeenageMutantNinjaTurtles'': Until "The Evil League of Mutants" and "Shadow of Evil", it seemed Lou Jitsu was only a film star that the Turtles and Splinter were merely fans of. The former episode revealed that he was a pre-mutated Splinter and the latter revealed that "Lou Jitsu" was merely a stage name and like [[WesternAnimation/TeenageMutantNinjaTurtles1987 his 1987]] and [[WesternAnimation/TeenageMutantNinjaTurtles2012 2012 incarnations]], he's a combination of SparedByTheAdaptation and CompositeCharacter as he's a still-living and mutated Splinter.

* Arsenal in ''WesternAnimation/YoungJustice'': it's very hard to describe him in any detail or even reveal his real name without giving away ''something'' about Red Arrow's TomatoInTheMirror twist from season 1.

** Simon Petrikov, aka the Ice King, is an interesting case of this, as the character has been in the show since Day One. However, nothing can really be discussed about him without mentioning the season three and four plot twists that completely turn the character and the show's universe on their heads: he's over a thousand years old, having lived as a antiquarian prior to [[WorldWarIII The Mushroom War]], and flashbacks to this era have him referencing real world locations and pop culture. He was the foster parent of Marceline until her early teens, and the magic crown he wore in order to protect himself and her was what drove him [[WithGreatPowerComesGreatInsanity to utter madness]] and made him unable to remember his life as Simon. Prior to "Holly Jolly Secrets" and "I Remember You", which revealed some of this information, Ice King was played more as a pure joke villain rather than a sympathetic character, Ooo's status as a post-apocalyptic Earth was just WordOfGod trivia instead of something important to the show's developing MythArc, and Marceline's own past was similarly shrouded in mystery. Talking about Simon Petrikov is necessary to explain an important part of the show's lore and why both Marceline and Ice King's behave the way they do.

* It's hard to talk about [[SecretIdentity The Blue Spirit]] in ''WesternAnimation/AvatarTheLastAirbender'' without spoiling that he's really [[PlayingWithFire Prince Zuko]].

* Numbuh 74.239 of ''WesternAnimation/CodenameKidsNextDoor'' is a member of the KND science team and initially was just another one of the recurring characters of the [[HeroesUnlimited many, many KND operatives.]] He got a big boost of importance in the sixth and final season as part of the unfolding "Splinter Cell" arc, and the viral campaign to get a KND sequel series takes this ''even further'' with the reveal that he was an undercover ''[[AlienAmongUs Galactic]]'' Kids Next Door operative all along. Speaking of, there's no way to talk about the ''G:KND'' animatic (An attempt to make a sequel/spinoff happen) without revealing that the Galactic Kids Next Door are possibly evil, or that Lizzie is really Numbuh Vine.
* ''WesternAnimation/{{Detentionaire}}'': [[IdenticalAncestor Lo Ping]], whose mere existence reveals the full extent of the Ping family's involvement in TheConspiracy, as well as the source of Lee's [[TheImmune immunity to the Prank Song]] and enhanced abilities.
* In ''WesternAnimation/{{Disenchantment}}'', all we know about Queen Dagmar is that she's Bean's MissingMom and TheLostLenore for Zog. In the last two episodes of season one we discover that she's not dead, just TakenForGranite, and that Zog's search for the Elixir of Life was to revive her. And ''then'' we find out that she's been EvilAllAlong.

** Just even ''mentioning'' that Della Duck is part of the reboot falls under this, as the show's first StoryArc covers her disappearance, and she joins the cast partway through the second season. The tie-in comics also featured prequel stories where she's adventuring with Scrooge and Donald very early on.

** ''Any'' F.O.W.L. operative outside of Black Heron is this, as the majority of the ones seen in the show so far were only [[WhamShot revealed]] to be F.O.W.L. operatives in the last seconds of the season 2 finale.

*** Two characters from the finale, May and June, are also this, given they have their backstories tied to Webby, adoptive family, and F.O.W.L.
* ''WesternAnimation/EdEddNEddy'' has Eddy's brother. He is made out to be TheAce by Eddy, but when he [[LastEpisodeNewCharacter actually]] [[WesternAnimation/EdEddNEddysBigPictureShow appears]] in TheMovie, it turns out [[BigBrotherBully that couldn't be farther from the truth]].
* Although they are now a case of ItWasHisSled and major FanficFuel, Tommy and Tammy Turner, who appeared in the DistantFinale to ''WesternAnimation/TheFairlyOddParents'''s ''WesternAnimation/ChannelChasers'' special, were this, as they show that in 20 years, Timmy would part ways with Cosmo and Wanda, grow up, get married, and have two children who would get Cosmo and Wanda as fairy godparents ([[{{Retcon}} unless you go by the live-action TV movies that came much later, that is]]).

** ''Everything'' about Amon is a spoiler, especially him really being Noatak, one of [[VillainousLegacy Yakone's]] children.
** Season Two has Unalaq, whose evilness was sort of obvious, but not to the extent of how far-reaching it was. But it also had [[CorruptCorporateExecutive Varrick]], whose MidSeasonTwist came out of virtually nowhere.

** [[ForcedIntoEvil Nooroo]] and [[TurtlePower Wayzz]], whose very existence reveals that there are active [[TransformationTrinket Miraculous]] users besides [[TheHero Marinette]] and [[TheLancer Adrien]].
** The Collector is difficult to discuss without revealing that he's [[FalseFlagOperation actually]] [[BigBad Hawk Moth]]. Furthermore, his identity as [[JerkWithAHeartOfJerk Gabriel Agreste]] was leaked ahead of time, but his identity as Hawk Moth [[WhamShot wasn't]].

** Twilight Sparkle, aka ''the show's main character''. There's no getting around the fact that she became a [[RoyalsWhoActuallyDoSomething Princess]] home at the end of the third season. Her new [[WingedUnicorn wings]] are dead giveaways.

** Diamond Tiara's mother [[AbusiveParents Spoiled Rich]], introduced in "Crusaders of the Lost Mark", is impossible to discuss without revealing that she's the reason Diamond is TheBully she is, Diamond's redemption, and how it leads the titular Cutie Mark Crusaders to receive their cutie marks. Naturally, the Cutie Mark Crusaders themselves serve as this after the episode as well.
** The Changelings are actually this trope TWICE, due to the entire species undergoing a HeelRaceTurn in the Season 6 finale, physically changing their appearance in the process. Thorax is a natural extension of this, as he's the TokenHeroicOrc who helped caused the change to begin with. Of course, talking about that episode is impossible without...
** Discussing [[IndividualityIsIllegal Starlight]] [[WellIntentionedExtremist Glimmer]]. Talking about the character after Season 5 is impossible without revealing that she pulled a HeelFaceTurn at the end of it and became the [[SixthRanger seventh ranger]] to the Mane Six.
*** To know of Sunburst's existence is to know of Starlight's FreudianExcuse for why she became evil. And to know of Sunburst is to also know of...

* ''WesternAnimation/OKKOLetsBeHeroes'' has [[PosthumousCharacter Laserblast]], [[MadScientist Professor Venomous]], and [[KnightOfCerebus Shadowy Figure]]. As of season 3, it's impossible to talk about any of them without revealing that [[TwoAliasesOneCharacter they're all the same person]], as well as [[LukeIAmYourFather K.O.'s father]].
* In ''WesternAnimation/OverTheGardenWall,'' the protagonists spend about half of the miniseries trying to find Adelaide of the Pasture, Good Woman of the Woods. It's hard to say much else about her without revealing that [[EvilAllAlong she's actually a]] WickedWitch who immediately tries to [[{{Brainwashed}} make them her slaves]].
** To a lesser degree, Auntie Whispers, the above's sister and opposite: seems like a fairy-tale style WickedWitch, but is actually GoodAllAlong ([[CreepyGood if still creepy]]).

** Tammy ends up this, as during Bird Person's wedding she's revealed to be an [[TheMole undercover agent for the Galactic Federation]], kills Bird Person, then resurrects him and leads the remnants of the Galactic Federation.
** Evil!Morty is this due to the fact that [[TheDogWasTheMastermind he is the one behind the abduction of various Mortys]] instead of Evil!Rick, who's revealed to be a robot built by him. He also gets elected as the president of the Citadel of Ricks in season three.
** [[UnfortunateNames Mr. Poopybutthole]] becomes one after Beth discovers that he was ''[[GoodAllAlong not]]'' a parasite after all.

* Mayor Jones, Angel Dynamite, Mr E and the Chileses in ''WesternAnimation/ScoobyDooMysteryIncorporated''. Even knowing that most of the tropes around these characters are spoilers probably counts as a spoiler! (Well, except Mr E, who's clearly hiding something from the beginning.) There's also the simple ''existence'' of the GreaterScopeVillain, who turns things [[GenreShift inside out and upside down]] by their mere presence.

** The fact that Ahsoka Tano, who first appeared in ''The Clone Wars'', appears at all is a massive spoiler.
*** Her return late in season 4 after being missing since the end of season 2 brings with it many more spoilers.

* Season 2 of ''WesternAnimation/WanderOverYonder'' introduces KnightOfCerebus Lord Dominator as a DarkerAndEdgier version of IneffectualSympatheticVillain Lord Hater. Good luck getting to the Season 2 premiere without prior awareness of the episode's final reveal that [[SheIsTheKing she's a girl]] [[SamusIsAGirl in a towering suit of masculine-looking armor]].

* ''WesternAnimation/EdEddNEddy'' has Eddy's brother. He is made out to be TheAce by Eddy, but when he [[LastEpisodeNewCharacter actually]] [[WesternAnimation/EdEddNEddysBigPictureShow appears]] in TheMovie, it turns out [[PsychopathicManchild that]] [[WouldHurtAChild couldn't]] [[JerkWithAHeartOfJerk be]] [[GrievousHarmWithABody farther]] [[SmugSnake from]] [[TheSociopath the]] [[BigBrotherBully truth]].

* Jonathan Rook in ''WesternAnimation/StretchArmstrongAndTheFlexFighters''. The revelation that he is Stretch Monster not only turns him from a benevolent benefactor into the BigBad of the series, but it also places his actions throughout the first season in a sinister new light. The reveal also changes the show's StatusQuo radically.

** Pink Steven mere ''existence'' is this. His formation answers a question fans have pondered for years about Steven's gem half, and with it, proves a major revelation in Rose Quartz; that she is ''gone'' and can never form again, concluding the show's [[MythArc major arc]].

* ''WesternAnimation/RoswellConspiracies'': Riniker's true identity.

** To a lesser degree, Auntie Whispers, the above's sister and opposite: seems like a fairy-tale style WickedWitch, but actually GoodAllAlong ([[CreepyGood if still creepy]]).

* Mayor Jones, Angel Dynamite, Mr E and the Chileses in ''WesternAnimation/ScoobyDooMysteryIncorporated''. Even knowing that most of the tropes around these characters are spoilers probably counts as a spoiler! (Well, except Mr E, who's clearly hiding something from the beginning.) There's also the simple ''existence'' of the GreaterScopeVillain, whom turns things [[GenreShift inside out and upside down]] by their mere presence.

** [[AbusiveParents Spoiled]] [[RichBitch Rich]], introduced in "Crusaders of the Lost Mark", is impossible to discuss without revealing that this is the episode where the titular Cutie Mark Crusaders receive their cutie marks. Naturally, the Cutie Mark Crusaders themselves serve as this after the episode as well.

** Wanna know why Diamond Tiara was the AlphaBitch we all knew? It was an upbringing by her mother, Spoiled Rich, who raised her to be one and not let anyone else get in her way.

* ''WesternAnimation/ReBoot'': Just seeing his character model makes it obvious that something traumatic happens to Enzo.