* In ''{{Mucha Lucha}}: The Return of El Malefico'', After El Malefico is beaten in the first fight, he transforms into a towering giant to continue the fight.
* At the end of ''DuckTalesTheMovieTreasureOfTheLostLamp'', the villain Merlock uses his talisman to transform himself into a [[OurGryphonsAreDifferent gryphon]] as an attempt to take away the titular magic lamp and use it to take over the world.
* ''WesternAnimation/DrawnTogether'': When the King of Mexico drinks the worm . . .
* In the ''TeenTitansTroubleInTokyo'' {{OAV}}, the human bad guy leaps into a tank of magical ink, turning into a giant inky monster with metal tentacles, constantly spawning four-color minions.
* A few characters on ''WesternAnimation/ThePowerpuffGirls'' pulled this trick. In the episode "Knock It Off", for example, Professor Utonium's slacker roommate from college, Dick Hardly, gets some [[GreenRocks Chemical X]] and starts making hordes of Powerpuff clones, renting them out to big cities as a new crime-prevention system. When the Girls learn about his scheme and confront him, he tries to hide the remaining Chemical X by swallowing it... and turns into a giant monster.
** Mojo became one giant ape in the Powerpuff Girls movie. Him also did this in the episode Speed Demon and Power Noia, though into two different forms. It actually works very well for HIM in Speed Demon and for Mojo in TheMovie. So does Sedusa when she tricks the Gangrene Gang into stealing three Egyptian artifacts for her. Not only does it restore her hair, it turns her into a giant, real-snake haired monster bent on destroying the Powerpuffs and Townsville. Remember, it's always about the tiara!
* On the ''OsmosisJones'' series, a corrupt mayoral candidate who has been illegally using growth hormones to sabotage his rival's campaign gets caught red-handed with the stuff, downs it in a panic, and you can guess the rest.
* Kevin 11 from ''WesternAnimation/{{Ben 10}}'' is an odd spin on this: His '''true''' form is his first form, [[spoiler:an orphaned eleven-year-old boy with the power to absorb energy. Attempting to absorb the Omnitrix's energy, however, resulted in him losing the only thing he had left... His humanity.]]
** Then again, there's more than one way to look at the phrase "true form":
--->'''Kevin:''' It's payback time for turning me into a freak!
--->'''Ben:''' You always were a freak, Kev. It's just that now the ugly's also on the outside.
** Fortunately for Kevin, [[spoiler:''WesternAnimation/Ben10AlienForce'' ends with the Omnitrix destroyed (which Ben replaces with the Ultimatrix) and Kevin regaining his humanity as a result]].
** In ''Ben10UltimateAlien'', Kevin absorbs the power of the Ultimatrix to stop an incredibly powerful villain, attaining a new one-winged angel form.
** Doctor Victor, from the third season finale, is another straight example, an absurdly large NASA scientist at first appearance but secretly a hulking FrankensteinsMonster-esque alien beneath the fašade.
*** The third season finale of ''WesternAnimation/Ben10AlienForce'' sees it happening a few times, with [[spoiler: Albedo's Ultimatrix being able to unleash the [[HollywoodEvolution "ultimate evolution"]] of the various alien forms. Ultimate Humongasaur is green and much stronger than the normal version, while Ultimate Swampfire is a tree with blue growths. And then once Vilgax's ship floods he unveils "his true form" - [[AnticlimaxBoss a giant squid/octopus]].]]
** An interesting [[JustifiedTrope Justified]] example occurs in the SpiritualSuccessor to ''WesternAnimation/{{Ben 10}}'', ''WesternAnimation/GeneratorRex''. Justified because the character who goes OneWingedAngel is a shapeshifter, interesting because [[spoiler:the hero, Rex, is the one who does it, admittedly in a flash back.]]
* Parodied with typical relish in a Halloween episode of ''WesternAnimation/SouthPark''. The spirit of Wall-Mart revealed his "terrifying true form"... by removing his stick-on moustache.
** Music/{{Korn}} (stay with us here) tried to do a heroic version of this during their guest appearance in another Halloween episode. It didn't quite work out. [[spoiler:"[[ThePowerOfRock Korn powers activate!]] Form of - [[BlessedWithSuck CORN!!!]]"]]
*** And in "Pandemic Part 2", there was an evil United States head of Homeland Security who, after revealing he was the leader of the guinea creatures, transformed into a [[spoiler:GUINEA PIRATE]].
** Ahem. [[Music/BarbraStreisand Mecha-Streisand]].
* [[SealedEvilInACan Hexxus]], the spirit of destruction in ''FernGully'', has three different monstrous forms. He starts out as a wad of toxic waste, turns into a cloud of poisonous gas, and finally appears as a burnt-looking skeleton covered in a cloak of pestilence.
* Characters, particularly Franchise/{{Batman}} villains, in the {{DCAU}} like this trope a lot as well:
** Clayface... it's easier to say he ''really'' liked to turn into horrifying things during combat;
** '''''[[PunctuatedForEmphasis "I!!! AM!!! BANE!!!!!"]]'''''
** One of the more way-out examples is the episode "Home and Garden", where Poison Ivy created a race of plant people who start out as normal-looking babies (save for the fact that they've emerged from giant seed pods) but may suddenly mutate into huge, green, ogrish thugs;
** Eventually it got to the point where the Preserver assumed a monstrous form to fight Lobo in the ''WesternAnimation/SupermanTheAnimatedSeries'' episode "The Main Man".
** It was even nastily subverted by the time the ''WesternAnimation/BatmanBeyond'' episode "Splicers" came along. The [[GeneticEngineeringisTheNewNuke evil scientist]] leader of the Splicers pumps himself full of LegoGenetics Juice, transforming into a fearsome monster combining the features of many creatures. Terry fights him normally for a bit, then gets the bright idea to inject ''more'' of the serum into the baddie, horribly mutating him into a blobby thing... [[spoiler:that is actually still quite capable of fighting and, worse yet, is even more powerful than before.]]
** Speaking of ''WesternAnimation/BatmanBeyond'', the writers liked this trope enough to play it fairly straight in every other episode. The episode "Curse Of The Cobra" is a good example; as a matter of fact it used LegoGenetics as well.
*** This is also the series where the writers admitted they would blow up the building if they couldn't figure out a good way to end an episode.
** In the terrible trio episode of ''WesternAnimation/TheBatman'', The Trio uses skin patches to administer the Langstrom serum. In the end Fox (a guy turned anthro fox) ends up turning into a griffin-like monster.
* In ''WesternAnimation/BikerMiceFromMars'', Fred The Mutant, Karbunkle's sidekick/assistant, is mixed up of different parts and absolutely loves pain. Another episode had a villain called Evil Eye Weevil, a skeleton like thing who is a NoCelebritiesWereHarmed parody of Elvis and UsefulNotes/EvelKnievel. Evil Eye Weevil could shoot a "hostility beam" at anyone and anyone hit by it would start fighting like crazy. Then again, the Plutarkians were never the picture of beauty either.
** In the 2006 revival, Stoker (the Biker Mice's mentor) turns into an insane rat-like monstrosity called "Stoker Rat" by the light of the sun due to radiation.
* Parodied in an episode of ''{{Catscratch}}''. While the brothers are watching a scary monster movie, they are interrupted by Human Kimberly at their door with a gift of broccoli. Gordon is fiercely allergic to the broccoli and he puffs up so bad that he [[CoincidentalAccidentalDisguise looks just like]] the monster in the movie. Mr. Blik and Waffle think he ''is'' the monster from the movie and run for their lives. When they can no longer run they are faced with their only option: fight the beast.
** It also subverted in the episode with the Banshee. The true form of the Banshee is revealed to be a "beautiful" seal woman - depicted as a seal with a dress and long blonde hair.
* Happens a lot in ''WesternAnimation/JackieChanAdventures''. This happens to anyone who wears one of the oni masks, and in the final season it happens to the villain Drago, or anyone else, who absorbs a demon power. When Drago gets ''all'' the demon powers, the end result is quite...[[{{Squick}} monsterous]]. Most people would probably say that Ultimate Power is not worth the price of looking so ugly.
* In ''CubixRobotsForEveryone'', the second main villain, a female CorruptCorporateExecutive who runs Rubix Corp, turns out to actually be an alien and in one episode reveals her true form.
** Even more squicky is that the alien sounded like a ''male''!
* In the ''WesternAnimation/DannyPhantom'' movie "Reality Trip", [[MonsterClown Freakshow]] turned into a large and grotesque ghost to combat Danny. He didn't realize it until the last minute that Danny [[TrickingTheShapeshifter tricked him into being a ghost so that he could easily suck him up in the Fenton Thermos]].
* In all versions of ''WesternAnimation/{{Spawn}}'', Violator eventually changes from his MonsterClown appearance into a huge horned monster whenever he wanted to smack some stupid out of Spawn.
* Spoofed in ''WesternAnimation/{{Igor}}'' where Jackyln runs out of pills and turns into her true form: a cute little Igorrette.
* ''TheFairlyOddparents'' has [[spoiler:The Lead Eliminator, who eventually morphs into the powerful Destructinator]] in the "Wishology" trilogy.
** Very earlier than that, we had Super Bike, a Cyborg-Like motorcycle with a Humanoid torso that greatly resembles a "''Hunk''" Superhero. However, if you [[BerserkButton piss him off]], and his human-half will turn into a mechanic, [[ScaledUp red-dragon monster]] that's more than capable to [[PlayingWithFire incinerate you]] [[NoHoldsBarredBeatdown while crushing you with his tires]].
* ''WesternAnimation/CaptainSimianAndTheSpaceMonkeys'' has "Gormungus", an alter-ego of GentleGiant Gor. For roughly the first third of the series, pushing Gor's BerserkButton sends him into an UnstoppableRage. After the malevolent alien Apax captures Gor and decides that the temper and strength make him the perfect gladiator, but that gentle side just has to go, he zaps Gor with a home-made mutagenic raygun. As a result, whenever Gor gets angry, he grows into a massive, more feral-looking gorilla creature, sort of a cross between TheIncredibleHulk and Film/KingKong, until he gets calmed down.
* This happened to Valtor in ''WesternAnimation/WinxClub''.
** And the Trix, in Season 2 (the Negatrix), Season 5 (their Dark Sirenix forms, which was a physical mutation instead of their usual costume change upgrades), and Magical Adventure (when the Ancestral Witches possess them).
** Tritannus, the main villain of Season 5, invokes this in the second episode of the season when he absorbs magically corrupted oil that gives him incredible magical power. Not only has he stuck around since then, but the One-Winged Angel form is what he's used for most of the season; he's pretty much useless when in his original body, though he typically has someone to protect him when that happens. His plan seems to be acquiring another such form, which cannot be good.
* In WesternAnimation/{{Chaotic}}, Aa'une went from glowing EvilOverlord to a giant monster with several tentacles when exposed to the energies of Lake Blakeer. Then in the next episode he goes down right EldritchAbomination by growing extra mouths and more tentacles.
** Promptly subverted when Iparu's shapeshifting power allows him to assume an identical form and match Aa'une blow-for-blow in his powered-up state.
* ''WesternAnimation/PhineasAndFerb'' makes a joke about this trope in the episode "Nerds of a Feather". A TV producer Dr. Doofenshmirtz has captured to pitch a TV idea to, who is voiced by SethMacFarlane, says that when the holographic monster that Phineas and Ferb have made comes out that "having monsters come out of no where at the end of stories is lazy story writing."
* ''WesternAnimation/AdventureTime'': If you dare press Marceline the Vampire Queen's BerserkButton, she turns into a giant rampaging bat.
* In a heroic version, ''WesternAnimation/AvatarTheLastAirbender'' has Aang and the Ocean Spirit bond to form a super-monster (nicknamed "[[FanNickname Koizilla]]" by the creators and fans). The [[SuperMode Avatar]] [[UnstoppableRage State]] might also count, but it's actually more of a [[SuperpoweredEvilSide Superpowered Good Side]] with GlowingEyesOfDoom....[[GoodIsNotNice It's still not safe to be near Aang when he's in the Avatar State, though.]]
** Interestingly, Hei Bai's One-Winged Angel form is the one in which we first see him. He has a normal form; it's just that the heroes arrive in the middle of his FreakOut.
** [[spoiler: Shows up in]] the SequelSeries ''WesternAnimation/TheLegendOfKorra'', when [[spoiler: Korra's EvilUncle merges with [[EldritchAbomination Vaatu]] to create the Dark Avatar. After he defeats Korra and destroys [[GodOfGood Raava]], he becomes a battleship sized Dark Spirit and proceeds to go on a rampage]].
* Galvatron from the ''{{Transformers}}'' series, an upgraded form of the series BigBad, Megatron.
** [[http://www.youtube.com/watch?v=TG4GaPcLgOs Unicron does it with style in the 1986 movie.]]
** [[spoiler:A human example with Silas]] in ''WesternAnimation/TransformersPrime''. [[spoiler:After being mortally injured when Nemesis Prime falls on top of him, his mind is transferred into the body of the recently killed Breakdown.]]
* Venger, from ''[[WesternAnimation/DungeonsAndDragons Dungeons & Dragons]]'', transforms into a monster in the episode "The Girl Who Dreamed Tomorrow".
* In the ''FostersHomeForImaginaryFriends'' [[TheMovie Movie]] ''Destination Imagination'', Mr. Herriman makes the mistake of verbally threatening an emotionally unstable RealityWarper named World with the thing he fears most, to be sealed away alone again. World replies by destorying his imaginary world and transforming into a massive chimera creature to try and reclaim Frankie, the only person in years who has treated him with kindness. It actually works out pretty well for him as no one can really stop him until Frankie calms the poor kid down.
* There is also ''WesternAnimation/AtomicBetty'' villain Maximus IQ becoming a giant demonic cat when he wore the Amulet of Shangra-La-Di-Dah in its titled episode.
* ''JimmyTwoShoes'' has this done...[[spoiler: by a GirlInTheTower Jimmy and Beezy spent the episode trying to rescue]].
* In the ''WesternAnimation/KimPossible'' series finale, Dr. Drakken is [[PlantPerson mutated by accidental exposure to a plant serum]]. This is initially PlayedForLaughs ("I look like a kid playing the flower in a school play!"), and then played straight as Drakken's vines prove powerful enough to defeat [[TripodTerror alien fighting machines]].
* ''MyLittlePonyAndFriends'': Lavan, villain of the "Quest of the Princess Ponies" serial, transforms to a powerful crystalline form by absorbing the magic of the six great {{Magic Wand}}s he stole from said Princess Ponies. His careless wresting of the power from the wands disrupts all the world's magic, meaning that doom is coming on two fronts.
* ''{{Thundercats}}'': "Ancient spirits of evil, transform this decayed form into MUMM-RA, THE EVER-LIVING!!" Snarf proves that anyone can channel the 'ancient spirits of evil' if they're allowed into the transformation chamber. This might seem disloyal of them, but hey, the spirits ''are'' evil...
* ''WesternAnimation/AaahhRealMonsters'' featured Ickis, a small red monster with an unfortunate resemblance to a bunny rabbit. He also comes from a long line of loomers, meaning he can size shift into a gigantic beast with red eyes and dripping fangs. For the humans he managed to scare, he definitely came across a One-Winged Angel.
* ''WesternAnimation/DexHamiltonAlienEntomologist'': When Zap's insect DNA overwhelms his human DNA, he transforms into a gigantic, monstrous insect form. Fortunately his friends are able to bring him back.
* In the ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' season four two-part finale ''[[Recap/MyLittlePonyFriendshipIsMagicS4E26TwilightsKingdomPart2 Twilight's Kingdom]]'', we get Tirek. He starts out a as a small, [[EvilSoundsRaspy raspy-voiced]] goatlike creature, a far cry from G1 Tirek, a monstrous centaur with an [[EvilSoundsDeep deep]] [[VoiceOfDramatic dramatic voice]] courtesy of VictorCaroli. But as he absorbs more and more magic, he goes through a string of OneWingedAngel forms, [[MakeMyMonsterGrow ending up a gargantuan, monstrous,]] {{kaiju}}-esque version of himself for the climax.
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