[[quoteright:180: [[WesternAnimation/SuperRobotMonkeyTeamHyperforceGo http://static.tvtropes.org/pmwiki/pub/images/tvtropes62_6299.jpg]]]]
[[caption-width-right:180:"You were right, [[TheGadfly Sprx.]] It ''is'' me. ''I've'' got TheVirus!"]]

Characters who decide to [[JumpingOffTheSlipperySlope toboggan]] down [[TheDarkSide The Dark Slide]] will have a fun time of it... at first. It starts small, maybe an EvilMakeover with SpikesOfVillainy and RedRightHand. But there's a nasty surprise at the bottom of this insidious slide; those who commit especially heinous crimes, abandon all of their humanity for power, or allow their inner darkness to bloom into a blight won't just grow [[CuteLittleFangs tiny]] [[FangsAreEvil fangs]] or discover EvilMakesYouUgly, they'll find out [[TitleDrop Evil Makes You Monstrous.]]

This is usually a feature of legends, both in real life and in stories. Basically, a guy, gal or even animal becomes so mean, malicious, and generally '''''Evil''''' that they transcend their mortal existence and become a monster of legend. A scourge on man and beast. After killing enough, the SerialKiller goes from a man into a force of nature that [[HealingFactor just]]. [[ImplacableMan Won't]]. ''[[BackFromTheDead Die.]]'' The [[WickedWitch witch]] buried in the heart of the woods will rise from her grave and haunt it as a half-dead corpse until her [[SoulJar spellbook is destroyed]]. The man who killed and ate his family out of hunger transforms into a {{Wendigo}}. The CreepyChild [[BullyingADragon everyone picks on]] lets the hatred fester and ferment until she becomes a living poltergeist.

Then again, the (mostly) innocent might suffer this fate because of a {{Curse}} or TheVirus. In the most extreme cases the character will no longer be flesh and bone but MadeOfEvil. While it's unlikely the character wants to seek redemption, it's not impossible that a loved one from before the change can at least give them pause.

Can also be caused through ThePowerOfHate. See also/compare OneWingedAngel and ScaledUp. ThePunishment is related, but the transformation into a monster is forced by an outside faction. Contrast PowerUpgradingDeformation, where monstrousness makes you powerful. Compare with CuteIsEvil where cuteness is the warning.

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!Examples:

[[foldercontrol]]

[[folder:Anime & Manga]]
* The evil humans fought by the DWMA in ''Manga/SoulEater'' are often incredibly bizarre. In the anime it's stated to be because eating humans souls was turning them to Kishin, whereas in the manga only weapons can eat souls, leaving their strangeness more or less inexplicable.
* ''WolfGuyWolfenCrest'': When [[spoiler: Chiba]] is taken over by his bloodlust and obsession with killing Haguro, he becomes a [[NightmareFace deformed ogre]] instead of a werewolf.
* ''{{Berserk}}'' has the [[EldritchAbomination Apostles]], every one of whom was once human before making their sacrifice to the Godhand and being reborn as demons.
* [[spoiler:The Witches]] in ''Anime/PuellaMagiMadokaMagica'' ''[[EldritchAbomination embody]]'' this trope.
[[/folder]]

[[folder:Comic Books]]
* {{Wendigo}}, particularly the MarvelComics version. (Only 98% though - the rabid man turns into Wendigo more or less permanently, not only on the anniversary.)
* In one issue of the [[ComicBook/TheLegendOfZelda Valiant Zelda comics]] Link steals the Triforce of Power from Ganon. As a result he starts turning evil, and nearly completely transforms into a piglike monster similar to Ganon.
* In ''TheLeagueOfExtraordinaryGentlemen'', [[JekyllAndHyde Dr. Jekyll]] indicates that Mr. Hyde has grown much larger from the exercise of sin.
* Marvel villain TheHood has a red hooded cape that gives him magic powers -- and is warping him into a demon.
* ''StarWarsLegacy'' Darth Krayt's own Vonduun Crab Armor(Yuuzhan Vong armor) has completely fused with his skin.
* Assuming that SelfDemonstrating/TheJoker started out as an ordinary man, whatever turned him into a Monster Clown certainly has this trope happen to him. However, in ''ComicBook/DeathOfTheFamily'', he has successfully outdone himself by first having his face removed, and then coming back one year later to wear it like a mask. Now he looks like a villain out of a SlasherMovie.
[[/folder]]

[[folder:Film]]
* This is the nature of Jason Voorhees in the ''Franchise/FridayThe13th'' series. Notably, he started out as an [[ImplacableMan implacable]] but very human killer, until he morphed into an immortal undead killing machine over time.
* Freddy Krueger of ''Franchise/ANightmareOnElmStreet'' somehow managed to become an undead dream-dwelling human monster just by being ''really'' nasty to kids. The [[Film/FreddysDeadTheFinalNightmare sixth film]] reveals that he was given his powers upon dying by several nightmare demons.
* ''Franchise/{{Halloween}}'s'' Michael Myers went from a [[SuperStrength super-strong]], [[TheSociopath sociopathic]] human with plans to kill his sister to a [[JokerImmunity completely unkillable supernatural being]] hell-bent on massacring half of Haddonfield. And if you follow [[Film/HalloweenTheCurseOfMichaelMyers the sixth movie's]] canon, his power is making him grow bigger in each movie.
* In ''Film/{{Doom}}'', Chromosome 24 turns evil people (or people with a great potential for evil) into monsters and those who aren't into superhumans. [[spoiler:Sarge, who had earlier crossed a moral line but was still just following orders,]] starts out superhuman after being infected but turns into a monster during his fight with Reaper the moment it seems like he's really going to murder him.
* ''Franchise/StarWars'': Darth Vader got all his flesh burned off and earned a black skull-faced suit. Darth Sidious was disfigured into a withered wrinkled ghoul of a man. Darth Maul got tattoos all over his body. Only Count Dooku got away in looks and stayed classy.
* Davy Jones from ''Franchise/PiratesOfTheCaribbean'' was supposed to use his supernatural ship, the ''Flying Dutchman'', to transport the souls of the dead to the afterlife. After his lover [[PhysicalGod Calypso]] abandoned him, he in turn abandoned his duties and began instead to bargain for the souls of dying sailors to become part of his undead crew, at which point they would be tortured until becoming one with the ship. This caused him (and, by extension, them) to mutate into horrific amalgamations of human and sea creature.
* [[spoiler:Theodora]] turns into an ugly green hag in ''OzTheGreatAndPowerful'' after [[spoiler:being tricked by her wicked sister Evanora (who is also an example) into eating a cursed apple]].
* According to ''HanselAndGretelWitchHunters'', any woman who turns evil and becomes a witch cannot perfectly hide her rotting flesh to a thorough examiner. Hansel uses it to prove that Mina is not a witch ([[spoiler:he turns out to be wrong, but the trope still applies because white witches like Mina are good and remain untarnished]]).
** Grand Black Witches can take on attractive forms, but when they use their powers they revert to their monstrous form.
* Chucky from the ''Film/ChildsPlay'' movies. The more time he spends in the Good Guy doll, the more evil the doll looks (as well as slowly mutating from plastic to actual flesh and blood).

[[/folder]]

[[folder:Folklore]]
* The concept is more or less universal amongst human cultures - literally regarding the inhumane as inhuman.
* This is one of the possible origins of a vampire, according to some accounts.
** And werewolves of the [[ImAHumanitarian cannibalistic]] SerialKiller type.
* This is also common in NativeAmericanMythology. Many, ''many'' monsters are spawned due to someone acting in such an anti-social fashion for so long that they become monsters.
** In the Native American mythology you may turn into a Wendigo if you become a cannibal.
* [[http://en.wikipedia.org/wiki/Fafnir Fafnir]] of NorseMythology, a dwarf who became so nervous about guarding his treasure that he became a dragon.
* [[http://en.wikipedia.org/wiki/Shuten-d%C5%8Dji Shuten-douji]] of JapaneseMythology, once an ordinary boy who callously burned up love letters and was cruel at heart. However, the smoke from this fire turned him into an [[http://en.wikipedia.org/wiki/Oni oni]].
[[/folder]]

[[folder:Literature]]
* Eustace in TheChroniclesOfNarnia, very allegorically becomes a dragon by being greedy and messing with a dragon's hoard.
* Waraug the evil dragon in [[EnchantedForestChronicles Dealing With Dragons]] turns into a frog after displaying un-dragonlike behavior.
* This happened to [[BigBad Lord Voldemort]] from ''Literature/HarryPotter''. He lost his handsome looks and acquired ugly snake-like features after using too much [[BlackMagic Dark Magic]]. He also made himself very, very difficult to kill through the same means.
* Tends to happen to the most powerful Dead in the ''Literature/OldKingdom'' books. The deeper regions of death have strongly metamorphic properties, so that any spirit that forces it's way back into the world of the living from there will have to be quite powerful to do so, but will no longer resemble its human form- and ''any'' dead spirit that willingly returns to life is a walking abomination against the natural order and a threat to any living person who encounters it.
[[/folder]]

[[folder:Live Action TV]]
* ''Series/BuffyTheVampireSlayer'':
** "[The Master] has grown past the curse of human features."
** Like the Master before him, Kakistos has grown past the curse of human features. Unlike the Master, he has cloven hooves in place of hands and feet.
* In ''Series/{{Supernatural}}'' Wendigo are created when humans dine on human flesh. The hunger grows and grows until they're nothing but beasts.
* In ''Series/KamenRiderDecade''[='s=] version of ''Series/KamenRiderHibiki'', an [[HenshinHero Oni]] who loses sight of [[ForGreatJustice justice]] and [[BloodKnight fights only to become stronger]] will become a powerful, corrupted, ox-like Makamou called Gyuuki. [[spoiler:This happens to Hibiki, forcing his young student Asumu to MercyKill him and take up the title of Hibiki.]]
** The line between monster and human is a common theme in Rider shows, since a lot of its heroes [[PhlebotinumRebel gained their powers from evil sources before using them for good]].
* ''Series/SamuraiSentaiShinkenger'', being heavily based on JapaneseMythology, has several bad guys who are explicitly ex-humans who went bad enough to become monsters. The villains for the show are even called Gedoushu, literally "Outside Path Ones", because they have left the path of humanity.
[[/folder]]

[[folder:Tabletop Games]]
* Fomori in ''TabletopGame/WerewolfTheApocalypse'' tend to be created when the Wyrm warps the flesh of those who are corrupt.
* Slashers in the ''TabletopGame/NewWorldOfDarkness'' are people who have done such evil things that the evil has warped them and given them special abilities to help them kill.
** In the same setting, the Mad are [[TabletopGame/MageTheAwakening mages]] who have committed so many heinous acts that their [[OurSoulsAreDifferent souls]] shatter, letting their magic start to leak out all over the place and manifest whatever psychoses pushed them over the edge.
** Similarly, the Centimani from ''PrometheanTheCreated''. Usually driven over the DespairEventHorizon by the raft of crap Prometheans have to deal with, they turn their back on [[ToBecomeHuman the Pilgrimage]] and start dealing with [[TheDarkSide Flux]]. This usually results in mutations. ''Lots'' of mutations.
*** That would explain the name.
* In ''TabletopGame/{{Warhammer}}'' and ''TabletopGame/{{Warhammer 40000}}'', worshippers of Chaos will inevitably mutate--sometimes rather quickly--as the power of Chaos seeps into their being. Chaos mutations tend to be rather...grotesque, even horrifying. Eventually, this power will be the key to the apotheosis into a [[EldritchAbomination Daemon]] [[AscendedToAHigherPlaneOfexistence Prince]], although failure or inability to keep the power from overwhelming oneself, leads to succumbing to the mutations and becoming a mindless [[BodyHorror Chaos Spawn]], which is a much more common fate (provided they survived to that point).
** The Dark Eldar of 40k, though they generally have a somewhat genteel evil look, have [[EvilScientist Haemonculi]], who enforce this trope ''on themselves'', with a combination of surgical and quasi-scientific means.
* In ''TabletopGame/DungeonsAndDragons'', a lot of TheUndead work this way. Cannibals rise from the grave as [[OurGhoulsAreCreepier ghouls]], unrepentant murderers come back as wights, those consumed by hatred become wraiths or spectres, and so on.
** There is also the taint mechanic introduced in the book "Hero's of Horror." In this you don't even have to do evil, mere exposure to evil can induce unpleasant effects.
** {{Ravenloft}} invokes this to the point of having game mechanics for it. Whenever a player character commits an evil act, the DM makes a secret roll to find out if this attracts the attention of the [[PowersThatBe Dark Powers]]. This normally results in gaining a supernatural power and a RedRightHand to go with it. Repeated evil acts lead to further progression down a chart, and a PC who reaches this stage becomes a monstrous NPC Darklord. Some [[MoralEventHorizon "Acts of Ultimate Darkness"]] can automatically take a character to Darklord status.
[[/folder]]

[[folder:Video Games]]
* In ''VideoGame/KingdomHearts I'', [[Disney/SleepingBeauty Maleficent]] embraces the Darkness and becomes a giant dragon as a result.
* As Sorceresses in ''VideoGame/FinalFantasyVIII'' grow older and continue to use their magic, their power begins to change their appearance into something less human and more monstrous. [[http://finalfantasy.wikia.com/wiki/Edea Edea]] was a fairly young sorceress so her appearance (while slightly altered) was still beautiful, whereas the older (and far crueler) sorceress [[http://finalfantasy.wikia.com/wiki/Adel Adel]] had morphed into a monstrous, muscular being. However, Sorceress [[http://finalfantasy.wikia.com/wiki/Ultimecia_%28Boss%29 Ultimecia's]] appearance is up for debate - her true form might be that of a [[EvilIsSexy sexy]], winged scantily-clad woman, or her true form might actually be her barely-human existence-sucking [[OneWingedAngel final]] [[http://finalfantasy.wikia.com/wiki/Ultimecia_%28Final_Boss%29 form]]. Considering how the other sorceresses look, the latter is more likely.
** Then there are the various sorceresses the player must fight during Time Compression. The [[http://finalfantasy.wikia.com/wiki/Sorceress_%281%29 first batch]] have odd skin colors and facial markings but still resemble beautiful women, the [[http://finalfantasy.wikia.com/wiki/Sorceress_%282%29 second batch]] look a little less human and have eerily [[EvilLaugh warped laughs]], while the [[http://finalfantasy.wikia.com/wiki/Sorceress_%283%29 final sorceress]] resembles a fat, bloated, purple slug.
* In ''VideoGame/FinalFantasyX'', this is how [[spoiler:one of Yevon's monks was turned into Omega Weapon]].
* ''Franchise/TheLegendOfZelda's'' Ganondorf, tapping into the full power of his Triforce of Power, transformed into the pig beast now known as Ganon. Although he is sometimes able to revert back to his human form at will, he definitely received the absolute refusal to actually stay down.
* In ''[[VideoGame/{{Diablo}} Diablo II]]'', the protagonist from the first opus, after defeating the eponymous Demon Lord, has put his soulgem on his own body in an attempt to contain his evil. As the game progress, Diablo takes over his body, gradually making him more monstrous until he turns back into the [[OneWingedAngel hideous]] [[EldritchAbomination Demon form]] Diablo used to assume.
* The further you go down the Dark Side in ''KnightsOfTheOldRepublic'', the uglier you get. When you're maxed out on [[KarmaMeter Dark points]], your eyes turn red and your skin gets ashen and veiny.
* In ''VideoGame/LiveALive'', this is the fate of [[spoiler:the knight Oersted]]. Originally one of the most straight up heroic player characters in the game, he [[FallenHero falls]] after he is betrayed and abandoned by everyone he knows. After accepting the mantle of "Demon King", he seems to prefer his new monstrous form to his original appearance. [[spoiler:He reverts to his original human appearance right before he [[DeathEqualsRedemption dies while warning the other heroes not to repeat his mistakes.]]]]
* [[{{VideoGame/TheElderScrollsVSkyrim}} Skyrim]] vampirism. A bite from a vampire will cause you to contract the disease that turns you into one but you have three days to cure it before you actually become one. So pretty much all vampires in Skyrim are vampires by choice.
** The fact that, in one quest, you meet vampires praying to Clavicus Vile to cure their vampirism, could be taken as indication that they were unwillingly turned into vampires. Or that they grew bored with it, who knows. Certainly vampirism is easy enough to cure before the three days have passed, a cure disease potion will do the trick, as will praying at a shrine.
* Isamu in ''VideoGame/ShinMegamiTenseiIIINocturne''. He decides to seek the truth by himself, not accepting ''any'' help... and next time you see him, [[spoiler:he's absorbing countless stray spirits in the Amala Network to empower himself]]. Result? [[spoiler:He ends up with ''dozens'' of faces growing out of his body]].
* Ryu from the ''VideoGame/StreetFighter'' series has an evil form, cleverly named "Evil Ryu". In the series, it is said that those who train in the art of Ansatsuken (Ryu's fighting style), they can tap into even more power with Satsui no Hadou, which causes the user to do anything for victory, including murder. Ryu using this power is what gave series boss Sagat, a gaping scar across his chest for sequels to come.
** Also worthy to note, series TrueFinalBoss Akuma has been cursed with the power of the Satsui no Hadou, causing him to lose his mindset and his humility.
* ''[[{{VideoGame/OFF}} OFF]]'' plays this one straight with [[spoiler: [[VillainProtagonist The Batter.]]]] [[MindScrew May]][[RuleOfPerception be.]]
[[/folder]]

[[folder:Web Original]]
* Th hideous Creature, a supervillain in the ''GlobalGuardiansPBEMUniverse'' has been active as a super-criminal since the 1930s. Originally he was an officer in the SS and a spy for Nazi Germany when he found a mystic artifact called the "Stone Heart" that legend said would grant the one who possessed it great power and immortality. But it also transforms you so that your appearance reflects your "true self". Unselfish heroes who are kind, honorable, and generous tend to become tall, attractive, and strong in physically perfect bodies. Its safe to say that Creature was '''''not''''' kind, honorable, or generous...
[[/folder]]

[[folder:Western Animation]]
* Gibson from ''WesternAnimation/SuperRobotMonkeyTeamHyperforceGo'' when he's infected with TheVirus in the episode "Thingy".
[[/folder]]

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