One-Winged Angel/Film

Kadaj, in Final Fantasy VII Advent Children, transforms into no less than the Trope Namer himself. Shortly after being super-Omnislashed, Sephiroth proceeds to show his lone black wing, before leaving Kadaj to go through the whole 'dying' process.
- In Advent Children Complete the wing appears before Sephiroth is Omnislashed, and he uses it to do a number on Cloud.
Shredder, at the end of the second Teenage Mutant Ninja Turtles movie, drank the mutagen, which transformed him into Super Shredder (also transforming his outfit). He attempted to destroy the Turtles along with himself by bringing the pier down on their heads.
- The Teenage Mutant Ninja Turtles cartoon that only aired in Japan (and has gained a bit of notoriety online as many viewers assume that it must be an elaborate parody). In this series, the Turtles were granted magical crystals that allowed them to transform into superpowered forms. Sadly, Shredder, Rocksteady, and Beebop found evil versions of the same crystals and are now capable of turning into superpowered monsters. At this point, it's probably better just to direct your attention to the show's opening sequence.
Happens all the damn time in Men in Black (both the comic, movies, and Animated Adaptation) whenever the disguised alien villains expose themselves in front of J and/or K. One has to wonder why they don't just shoot before the transformation is complete, what with the guns usually loaded and pointed at the alien during the transformation.
- However, they may be following the grand tradition of movie aliens flipping out and assuming monstrous forms to attack. The Thing does it (quite a lot really). So does Sil in Species.
- For the film, it was justified since the Bug had eaten the galaxy and shooting him would probably have destroyed it.
Happens to the villains in both 2003's Hulk and 2008's The Incredible Hulk. Then again, this makes sense as The Hulk himself could qualify as the heroic version.
In one of the Alien Nation films, the Big Bad takes a massive overdose of the MacGuffin slave-drug, seemingly dying, and then...
In the film version of The League of Extraordinary Gentlemen, The Dragon consumes enough of Jekyll's serum to tower over the real Mr. Hyde.

Mr Hyde: Not the whole thing!

Appears out of freakin' nowhere in the Lost in Space movie. Dr. Smith is attacked by an alien bug and somehow this transforms him into a distracting CGI creature. Bonus points for Lampshade Hanging the "well, we couldn't kill you as a human but now that you're a monster you're fair game" issue!
An early idea for The Lord of the Rings grand finale was to show Aragorn battling Sauron in the last battle. Sauron (just an gigantic red eye up to this point) would first be seen as a tempting angelic bishonen (Kate Winslet in cameo) who then transform into the gigantic armored fighter seen in the first movie's prologue. The filmmakers eventually decided that this was silly (and an inconsistency, since they had decided that Sauron wasn't supposed to be powerful and capable of fighting without his ring) and replaced the armored Sauron with a troll.
- There was a captivating piece of concept art for the "pretty-boy" Sauron: an angelic albino possessing an otherwordly beauty...except for his eyes, fiery red-on-black, exactly like the flaming eye of his other form. Furthermore, a close look at his face reveals that the flesh around his eyes has subtly began to crack like plaster...
  - This is because Sauron is a Maia (angel), sort of like Gandalf. The beautiful side was his original form and he used it to corrupt Aragorn's ancestors. Eru Ilúvatar destroyed Numenor and Sauron lost his body. He recovered, but could never regain his beautiful form and had come up with a badass one instead. Thus the above scenario would have violated canon, but that probably wouldn't have bothered the film makers since they had already swapped Sauron's physical book-form for a giant red eyeball.
Dracula and his brides in Van Helsing can turn into harpy-esque bat things. And in the finale, Van Helsing himself becomes a werewolf to battle Dracula, who has turned into a giant demon thing.
In the 2002 live action Scooby Doo movie, Scrappy(!) turns into a demonic version of himself with razor sharp claws and teeth, a big muscular body, wild looking eyebrows, enhanced agility and strength- A DEEP BOOMING VOICE and a horrid case of bad breath.
According to the bonus features on the DVD of the first Blade movie, this was the original ending of the film, with villain Deacon Frost transforming into the blood god La Magra (who looked like a giant CGI red tornado). However, the filmmakers were struck with a jolt of good sense and realized that it would detract from the climax, having just spent the entire film building up Frost as the main villain. Instead, La Magra possesses Frost, granting him nigh-invincibility and fighting prowess.
- Played straight with Dracula in the third film.
Tim Burton has used this trope a few times:
- In Beetlejuice the titular character turns into a variety of bizarre things to frighten people, as do Adam and Barbara.
- Parodied in Big Fish. The hero suspects the ringmaster is a werewolf and dreads the inevitable transformation. Turns out he is - but not a mean or monstrous one. The werewolf does bite Edward, but then he apologizes after he turns back into a human.
- As mentioned in the Western Animation section below, The Joker loved revealing his Monster Clown face. This is due to a scene in the 1989 Batman film where Viki Vale (Kim Basinger) sprays water on The Joker's (Jack Nicholson) face revealing his Monster Clown look under the makeup and The Joker quotes the witch from The Wizard of Oz.
- The Penguin in Batman Returns is another non-fantastic example. As a derelict living in the sewers, he wears nothing but a thick robe over slime-stained long underwear. Once he decides to compete in Gotham City's mayoral race, he begins appearing in public in a tuxedo shirt, a waistcoat, striped pants, a bow tie, and a top hat. Fleeing the city in disgrace after his hypocrisy is exposed by Batman, Penguin loses his hat and retreats back into the sewers, where he begins stripping off his fancy suit. For the rest of the movie, he appears only in his robe-and-long-underwear combo - signaling that he has returned to his "normal," quasi-animalistic self.
Some of the monsters in the Godzilla series can change form. For example, in Godzilla: Final Wars, Monster X transforms from a skeletal dragon into the more powerful Keizer Ghidorah (Which is essentially an Expy of both King Ghidorah and Desghidorah (a quadrupedal three-headed dragon Kaiju)).
- Likewise, there's Destoroyah who changes from a pretty dang big crab/scorpion-esque monster into what looks like a kaiju version of The Devil that towers over Godzilla himself.
In Lisztomania, Richard Wagner turns into a grotesque vampire at the final showdown with Franz Liszt.
In Tenacious D in The Pick of Destiny Paul F. Tompkins changes into Satan and KG and Jables challenge him to a rock-off.
Ghostbusters has the scene at the begining where the librarian ghost turns into a hideous ghoul when the GBs are trying to get her. Interestingly enough, there was an earlier librarian ghost puppet that got rejected because it was too scary, but it was recycled and used in the 1985 vampire film Fright Night (see below).
- Parodied at the end when Gozer, who initially appeared as a young woman, demands the Ghostbusters choose the form it will use to destroy them. All the GBs clear their minds except Ray - who unintentionally thinks of the Stay-Puff Marshmallow Man.
The Witches of Eastwick has the scene where Jack Nicholson's character becomes a giant and then after the girls smash the wax voodoo doll of him becomes a worm-like monster.
In the 1985 vampire film Fright Night the vampires have three phases of transformation, the first is typically like a normal human, the second is like a normal human but with fangs, and the third phase is a extremely crazy looking monstrous creature with More Teeth Than the Osmond Family. At the end Jerry Dandridge (the main vampire) turns into a human/bat hybrid thing, gets hit by sunlight and bursts into flames and finally dies. Interestingly enough, the vampiric version of Amy is in fact a recycled version of the rejected librarian ghost from Ghostbusters.
Resident Evil Extinction has the big bad evil scientist injecting himself with a massive dose of secret formula and then mayhem ensues. So does "Resident Evil: Degeneration" Except that in Degeneration, he was more of a Well-Intentioned Extremist, who's plan was to go on a rampage, exposing the research on the G-virus that was being done.
In The Film of the Book of Coraline, after The Other Mother loses her temper with Coraline and tries to stop her from escaping, she gets less and less human-looking. At first, she simply becomes inhumanly tall and gaunt; at the climax, she turns into what is best described as a spider-woman with giant sewing needles for limbs.
The main villain in the 1980s Eddie Murphy Vehicle The Golden Child spends most of the film looking like actor Charles Dance. At the Final Battle, and with no foreshadowing anywhere in the film, he transforms into a large, bony, winged demon (stop-motion animated to boot), whereupon Murphy kills him with a special knife.
At the climax of Enchanted, Queen Narissa uses her magic to turn herself into a large dragon and plans to kill everyone.
- As a shout out to Sleeping Beauty, no less.
Eddie Quist's transformation into a werewolf near the end of The Howling could be called this.
Toward the end of Conan the Barbarian (1982), the villain Thulsa Doom (played by James Earl Jones) turns into a snake to emphasize his inhumanity, though Conan doesn't actually fight him in that form.
At the end of the stop motion film, Jack the Giant Killer, after several attempts to kill Jack (the main character) are foiled, Pendragon, the main villain and evil sorcerer, transforms into a dragon to fight Jack, who eventually kills him in the final battle.
In Return to Oz, once Dorothy begins guessing right at the ornaments and restoring the Scarecrow, Tik Tok, and Jack to their original forms, the Nome King, previously human-sized and at one point almost looking entirely human, becomes a giant rock monster and attempts to eat them all. Unfortunately for him, Billina was inside Jack's head, and laid an egg, which fell into his mouth... POISON... TO... NOMES!!!
At the end of the first Guyver movie, Fulton Balcus, the head Zoanoid, turns into a giant creature after the main character refuses his invitation to join Chronos. The transformation is shown in the dark. All you can see are his Glowing Eyes of Doom, as they raise and separate to show just how big he has become. To his credit, taking him down requires the Guyver to use his secret weapon - a Wave Motion Gun in his chest.
- In the sequel Guyver 2: Dark Hero, Crane, a reptile zoanoid and main antagonist, gets his own (though damaged) guyver unit and turns into bad-ass incarnate.
At the climax of All Dogs Go to Heaven 2, Red assumes his gigantic true form after capturing all the dgos in Heaven with Gabriel's Horn. Truthfully, it's just an incredibly massive and more demonic version of his base form, but is still enough to prove a major problem... until Charlie discovers his weakness.
During the final battle of Ultra Galaxy Legend The Movie, Ultraman Zero manages to defeat Ultraman Belial by throwing him into a pit of lava. He's soon followed by the souls of his 100 kaiju, merging with them to form the 100 Union Kaiju Beryudora. It takes an all out attack from the Ultras, EX Gomora, and Ultraman Zero to finally put him down. And Belial still survived!
- In the sequel, Belial absorbs a massive amount of energy crystals he was stealing, transforming into the gigantic and monstrous Arch Belial.
In the first Hellboy film, every time Rasputin dies, a little bit more of his god comes with him, until at the end of the film, he dies one last time, his body splits open, and a full-fledged Eldritch Abomination emerges.
In the climax of Hop, holding the egg of destiny transforms Carlos into a giant, freakish bunny/chick amalgamation.
* In Windigo Slender Man is seen primarily as a man in a Nice Suit...until the climax where he unleashes his Combat Tentacles and starts throwing around vehicles.