* The plot of ''FanFic/InnerDemons'' is driven by a prophecy that Twilight Sparkle will succumb to the [[EnemyWithin darkness in her heart]] and become the "Queen of Darkness", who will [[TakeOverTheWorld take over all of Equestria]]. This happens within half a dozen chapters, and Queen!Twilight proceeds to take up the mantle of BigBad for the story.
** Trixie starts out the story as TheAtoner, who wants to learn true magic from Twilight in order to make up for her boastful and arrogant past. When Twilight turns, she talks Trixie into helping strike at the other Elements of Harmony... then Trixie sees [[InLoveWithYourCarnage how powerful Twilight is]], and performs a full turn herself in order to convince Twilight to keep her.
** In a rather ShockingSwerve, [[spoiler: Sweetie Belle and Scootaloo]], who join up due to a combo of MoreThanMindControl and not seeming to be fully aware of what's happening.
* In the ''FanFic/PonyPOVSeries'', [[spoiler:Fluttershy suffers a severe BreakTheCutie and falls victim to the same corruption as Nightmare Moon, transforming into the BigBad of the story arc, Princess Gaia/Nightmare Whisper.]]
** There's also the [[BadFuture Dark World]] versions of the [[BrainwashedAndCrazy Discorded]] Mane Six, who [[BigBad Discord]] uses as his CoDragons for a thousand years [[spoiler: until Cadence's spirit helps Twilight remember her true self, beginning the eventual {{Heel Face Turn}}s of all of them]].
** [[spoiler:The Nameless Passenger turns out to be a version of Twilight who turned into a [[HeWhoFightsMonsters vengeance crazed]] [[SuperpoweredEvilSide Nightmare]] seeking to punish Discord for all eternity via GroundhogDayLoop, no matter how many lives she may ruin or erase in the process.]]
* The entire plot of ''FanFic/QueenOfAllOni'' is kicked off when Jade's SuperPoweredEvilSide, the Queen of the Shadowkhan, is reawakened, setting Jade up as the BigBad.
** In the second half of the story, [[spoiler: Jade [[BrainwashedAndCrazy brainwashes Viper]] into being her new Samurai Khan General, Hebi.]]
* In ''FanFic/{{Respect}}'', [[spoiler:[[SmilePrettyCure Yayoi Kise]] undergoes a turn from sweet, timid, cybaby artist to berserk supervillain due to severe guilt and SanitySlippage.]]
* In the Power rangers fanfic [[http://www.fanfiction.net/s/6090657/1/Red_Poison Red Poison]] this happened in a parallel reality in which Jason switched sides out of jealousy of Tommy.
* Literature/SherlockHolmes in ''Fanfic/ChildrenOfTime'', as the combined end result of a BreakTheCutie experience and a SadisticChoice. He later tells [[AscendedFangirl Beth Lestrade]] that he was "curious". Her [[ThePowerOfLove unconditional love]] and HeroicSacrifice force him to truly ''[[HeelRealization understand]]'' what he's become and what he's done to her.
* [[spoiler: Bondís supposed informant]] in ''WebVideo/DiamondsCut'', a ''Film/JamesBond'' fan film.
* ''FanFic/{{Horseshoes and Hand Grenades}}'' has Gentaro do one when [[ForWantOfANail Kengo didn't revive him.]] A being known as Ophiuchus resurrected him and brainwashed him to believe that his friends wanted him to die and left him to the hands of Ryusei Sakuta/Kamen Rider Meteor. Things get ''very'' bad.
* Happens in the HungerGames fanfic ''Fanfic/SomeSemblanceOfMeaning'', when [[spoiler: Phlox allies herself with Vale, Fen, and Lark, only to attempt to murder them in their sleep. Thankfully, this fails.]] However, Vale thinks to herself later on that, in spite of [[spoiler: her]] actions, [[spoiler: Phlox]] wasn't really evil; it wasn't the ''right'' thing to do, but "this is [[BlackAndGrayMorality the Hunger Games]]. We all do things that we don't want to do--like killing and stealing and betraying--because let's face it: every single one of us wants to escape this sadistic prison the Gamemakers set up for us, to make it home alive. To our friends and families. For that, we would do anything."
* Maylu in ''Anime/MegaManNTWarrior'' fanfiction, ''[[Fanfic/MaylusRevenge Maylu's Revenge]]''.
* Tambryn in the HungerGames fanfiction ''FanFic/{{Claustrophobia}}'' started off as a nice, well-liked character. [[spoiler: Then she went off the deep end and tried to crucify her ally and district partner Maxim, who was only thirteen.]]
* The whole first instalment of the SonOfSunsTrilogy is an extended FaceHeelTurn for [[spoiler: Luke Skywalker]].
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