One-Winged Angel/Western Animation

"Maleficent: Now shall you deal with me, O Prince, and all the powers of Hell!"
 * Disney loves this Trope:
 * The Queen's "perfect disguise" in Snow White certainly counts, depending whom you ask; it's absolutely terrifying enough and--more importantly--it reflects the Queen's true nature. Supremely ironic given that the Queen wants to be "Fairest of Them All".
 * In Sleeping Beauty Maleficent turns into a dragon to fight Prince Philip, respectively.

""Remember me, Eddie?! When I killed your brother, I talked JUST! LIKE!! THIIIIISSS!!!!!"
 * Disney parodied that scene as early as The Sword in The Stone, when Mad Madame Mim comes very close to ending her Wizard's Duel with Merlin by turning into a goofy-looking Dragon.  Given how germs work, this means that her body is full of millions of tiny transformed Merlins....
 * In The Great Mouse Detective, Ratigan reverts to his monstrous feral rat formas part of his Villainous Breakdown. He proves incredibly dangerous, nearly killing Basil.
 * In The Little Mermaid, when, Ursula uses it to turn into a giant version of herself. Then
 * In Aladdin Jafar turns into a giant cobra, then into an "all powerful" genie. The thing is, Aladdin actually tricked Jafar into wishing he was a genie, so he'd be trapped in a lamp.
 * This seems brilliant only in the context of the rules set by the film; Aladdin used a Chekhov's Gun of a comment of the genie's back at the oasis. The actual djinni even in the proper translated Thousand And One Nights are enslaved in precisely one story: Aladdin, which features a 'slave of the ring' and a 'slave of the lamp.'
 * There was a mysterious slave from nowhere that dumped the transformed fish in the fire in 'The Fisherman and the Genie.' He may have been a genie himself, although the title character was just shut up in a jug so long he resolved to kill whoever let him out.
 * Appropriately for an Affectionate Parody of their own movies, the villain of Enchanted turns into a big dragon who will NOT shut up.
 * "You're crazy!" "No. Spiteful, vindictive, VERY large but never crazy."
 * Parodied in The Emperors New Groove: Yzma is exposed to one of her own potions, and emerges laughing maniacally from a huge cloud of smoke only to be revealed as....
 * In an even more comical version, Kronk's New Groove features Yzma using a potion that will turn her into something that her enemies (in this case a bunch of old people who she sold fake potions to) cannot harm... a cute little bunny. Unfortunately for her, while they don't harm her, the local condor doesn't mind taking her for food.
 * In one episode of the Emperor's New School Yzma does turn into a giant snake. And in another episode she and Kuzco have a transformation potion duel--one of the things Yzma turns into is a Tyranosaurus Rex.
 * And she once made a potion that would turn her into the most hideous, terrifying thing imaginable, so frightening the other wouldn't be able to do anything about her... comically subverted when she transforms into herself.
 * Judge Doom in Who Framed Roger Rabbit is almost a sick parody of the "Look at my true form and despair" variation.

"Kevin: It's payback time for turning me into a freak!
 * At the end of Duck Tales the Movie Treasure of The Lost Lamp, the villain Merlock uses his talisman to transform himself into a gryphon as an attempt to take away the titular magic lamp and use it to take over the world.
 * Drawn Together: When the King of Mexico drinks the worm . ..
 * In the Teen Titans Trouble in Tokyo 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 The Powerpuff Girls pulled this trick. In the episode "Knock It Off", for example, Professor Utonium's slacker roommate from college, Dick Hardly, gets some 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 The Movie. 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 Osmosis Jones 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 Ben 10 is an odd spin on this: His true form is his first form,
 * Then again, there's more than one way to look at the phrase "true form":

Ben: You always were a freak, Kev. It's just that now the ugly's also on the outside."


 * Fortunately for Kevin,.
 * In Ben 10 Ultimate Alien, 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 Frankenstein's Monster-esque alien beneath the facade.
 * The third season finale of Ben 10 Alien Force sees it happening a few times, with
 * An interesting Justified example occurs in the Spiritual Successor to Ben 10, Generator Rex. Justified because the character who goes One-Winged Angel is a shapeshifter, interesting because
 * Parodied with typical relish in a Halloween episode of South Park. The spirit of Wall-Mart revealed his "terrifying true form"... by removing his stick-on moustache.
 * 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.
 * 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.
 * Ahem. Mecha-Streisand.
 * Appropriately for a film that (ahem) was an intentional homage to the classic films, the villain in The Swan Princess has the ability to become "The Great Animal". His monstrous true form was teased throughout the entire movie until the very end - only to have him bring the Narm and change into what appears to be a big fruitbat.
 * Don Bluth likes Disney movies as well and has used this at least twice:
 * In the already insane Rock a Doodle, the Grand Duke appears to puke his evil magic up all over himself and mutates into a sort of gigantic owlish... tornado-ish... thing...
 * The spin-off movie Bartok the Magnificent has Ludmilla (voiced by Catherine O'Hara of SCTV) steal a potion that Babayaga has given Bartok to aid him in his quest - it turns you into whatever you are, deep down inside. She drinks it and...
 * Don Bluth actually worked for Disney around the time of movies like The Rescuers, so he was just carrying on the tradition.
 * Red, the demonic cat in All Dogs Go to Heaven 2 has three forms. One is an old looking dog with green eyes that have NO PUPILS. Another is a red demonic cat-jaguar...thing that wears a cape. His third and most powerful form is when he grows to ridiculous size and has his eyes glow bright red. Did I mention that he never shuts up?
 * Hexxus, the spirit of destruction in Fern Gully, 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 Batman Villains, in the DCAU like this trope a lot as well:
 * The Joker loved disguising himself and then revealing his true Monster Clown face (he's better known for doing this in The Movie);
 * Clayface... it's easier to say he really liked to turn into horrifying things during combat;
 * "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 Superman the Animated Series episode "The Main Man".
 * It was even nastily subverted by the time the Batman Beyond episode "Splicers" came along. The evil scientist leader of the Splicers pumps himself full of Lego Genetics 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...
 * Speaking of Batman Beyond, 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 Lego Genetics 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 The Batman, 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 Biker Mice From Mars, 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 No Celebrities Were Harmed parody of Elvis and Evel Knievel. 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 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.
 * Monster House contains one of the most bizarre versions of this ever. Bizarre, because the Big Bad in question is a house that has transformed into a monster.
 * Happens a lot in Jackie Chan Adventures. 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...monsterous. Most people would probably say that Ultimate Power is not worth the price of looking so ugly.
 * In Cubix Robots for Everyone the second main villain a female Corrupt Corporate Executive 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 it was a male!
 * In the Danny Phantom movie "Reality Trip", Freakshow turned into a large and grotesque ghost to combat Danny. He didn't realize it until the last minute that Danny tricked him into being a ghost so that he could easily suck him up in the Fenton Thermos.
 * In all versions of Spawn, Violator eventually changes from his Monster Clown appearance into a huge horned monster whenever he wanted to smack some stupid out of Spawn.
 * Spoofed in Igor where Jackyln runs out of pills and turns into her true form- a cute little Igorrette.
 * The Fairly Odd Parents has  in the "Wishology" trilogy.
 * Captain Simian and The Space Monkeys has "Gormungus", an alter-ego of Gentle Giant Gor. For roughly the first third of the series, pushing Gor's Berserk Button sends him into an Unstoppable Rage. 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 The Incredible Hulk and King Kong, until he gets calmed down.
 * This happened to Valtor in Winx Club.
 * Aa'une went from glowing Evil Overlord to a giant monster with several tentacles when exposed to the energies of Lake Blakeer. Then in the next episode he goes down right Eldritch Abomination 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.
 * Phineas and Ferb 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 Seth Macfarlane, 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."
 * Adventure Time:If you dare press Marceline the Vampire Queen's Berserk Button she turns into a giant, rampaging bat.
 * In a heroic version, Avatar: The Last Airbender has Aang and the Ocean Spirit bond to form a super-monster (nicknamed "Koizilla" by the creators and fans). The Avatar State might also count, but it's actually more of a Superpowered Good Side with Glowing Eyes of Doom....It's still not safe to be near Aang when he's in the Avatar State, though.
 * Koizilla is 'heroic,' but it also appears to have sunk most of the Fire Nation fleet, plunging thousands of naval personnel into the polar waters. Even assuming some vessels survived and were able to perform rescues and that the Water Tribe took a bunch of hostages for ransom, that still leaves the biggest kill count of the series on the Technical Pacifist hero. The season two finale, on the other hand, featured a villain winning the biggest city in the world: with zero casualties.
 * Said villainess then went to suggest performing genocide on the entire Earth kingdom, meaning that she was only saving those people to kill them letter. Also Koizilla didn't appear to kill anyone (Zhao doesn’t count, that happened only after the spirit left Aang), seeing that if he did went on a rampage, not a single soldier would have managed to escape to the ships, yet many, if not all the Fire Nation ships managed to flee with Koizilla just looking at them from afar. If you want to get picky, all those soldiers that weren't killed would go on to further attack Aang and the earth kingdom again in the future, so there's really no moral choice here.
 * Interestingly, Hei Bai's One-Winged Angel form is the one we first see him in. He has a normal form, it's just that the heroes arrive in the middle of his Freak Out.
 * Galvatron from the Transformers series, an upgraded form of the series Big Bad, Megatron.
 * Unicron does it with style in the '86 movie.
 * in Transformers Prime.
 * Venger, from Dungeons and Dragons transforms into a monster in the episode "The Girl Who Dreamed Tomorrow."
 * In the Fosters Home for Imaginary Friends Movie Destination Imagination, Mr. Herriman makes the mistake of verbally threatening an emotionally unstable Reality Warper 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 Atomic Betty villain Maximus IQ becoming a giant demonic cat when he wore the Amulet of Shangra-La-Di-Dah in its titled episode.
 * Jimmy Two Shoes has this done....
 * In the Kim Possible series finale, Dr. Drakken is mutated by accidental exposure to a plant serum. This is initially Played for Laughs ("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 alien fighting machines.
 * In the season 2 finale of My Little Pony Friendship Is Magic,
 * Thunder Cats "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...