Carl: [confused] Speak English, moron!
Witch: [exasperated] I'm turning you into your costumes.
Homer: Well, are ya gonna talk about it or are you gonna do it? [zapped]
It's All Hallows' Eve (usually) and the kids are trick-or-treating and everything is normal, but something magical is afoot, and turns people into whatever costume they are wearing. If you're dressed up as a werewolf, for example, you'll become an actual werewolf.
You'd be surprised just how often this happens in fiction.
Not to be confused with Becoming the Mask or Evil Costume Switch. Can overlap with The Mind Is a Plaything of the Body, which is bad news. Related to Evil Mask. Hilarity might ensue if overlapped with For Halloween, I Am Going as Myself.
May be the subject of a Halloween Episode.
- In Berserk, the leader of a cult dressed in a goat's head and used a snake as a fake penis. He gets transformed into an Apostle Spawn, which turns him into a real goat-headed, satyr-like monster with a snake for a penis. Before his transformation he was about to perform a sexual ritual with Casca, who was believed to be a goddess by the cult. After transformation the only thing he can think of is raping her. Luckily for her, he runs into Guts.
- Therefore, Repent!: At least one character transforms thus.
- Hellblazer: Happens at a revived pagan festival, to the detriment of everybody. (New father in baby costume to infant: "You're taking all of mummy's attention and it's! not! fair!" *splat*; a dentist(?) with a rictus grin mask wants EVERYONE TO SMILE!). This isn't transformation, but rather a crazy-making signal coming from the nearby underground nuclear base. John and his friend discover that loud punk rock cancels the effect a little too late: an ex-fighter pilot is "cured" just seconds after he releases a bomb, destroying the town and everyone in it (except John, of course).
- The Underburbs: This is part of the premise and Played for Laughs. The main character, Angie, and her mother turn into witches, and her brother into a monster. None of this affects life in the town very much.
- Doctor Who Magazine has one issue where the backstory involves all the nobles of a planet being turned into the animals that they dressed up as in celebration of surviving a plague that killed ten thousand peasants.
- The focus of the Yet Another Halloween Fic a.k.a. YAHF in Buffy the Vampire Slayer fanfiction.
- Like Buffy fans before them, the My Little Pony: Friendship Is Magic community made this popular as a way to make their characters into powerful villains, or, less commonly, heroes.
- RainbowDoubleDash's Lunaverse: Costumes revolves around this trope. In an attempt to promote her wares, Rarity uses a Zebrican ritual which she thinks will make her costumes more realistic. Unfortunately, in something of a Running Gag for the Lunaverse, she misunderstands the function of the ritual — it was designed to allow a zbra to take on the physical form and powers of a totem. So everyone wearing one of Rarity's costumes (and most of Ponyville was wearing one of Rarity's costumes) is transmuted into whatever they were dressed up as, and gains whatever abilities they subconsciously believed their new form should have. Rarity, for example, is turned into a vampony and gains hypnotic eyes and blood-sucking fangs. To make matters worse, the spell also causes all the victims to believe that they actually are whatever they'd been dressed as. Luckily, Trixie and Twilight had made their own costumes, and are able to dispel the curse. But not before several adventures occur...
- Snips and Snails had dressed up as Captain Equestria and Spiderstallion respectively, while Raindrops was in disguise as Princess Platinum. When Raindrops!Platinum is kidnapped by a pack of diamond dogs (formerly the workers of Sweet Apple Acres), the two superheroes rescue her. Snips!Captain even gets a kiss out of it... right as the magic's dispelled, so Raindrops ends up kissing Snips.
- Cherilee, dressed up as and turned into Catmare, attempts to rob a jewelry store before running afoul of Batstallion (formerly Heavy Roller) and Robin (formerly Scootaloo). After an innuendo-laden fight, they successfully catch her, only for Carrot Top to show up transmuted into Poison Ivy. Carrot!Ivy takes Batstallion prisoner with her spores, expressing an interest in feeding him to her plants. Cherilee!Catmare can't have that, as she has her own designs on Batstallion's body. The ritual comes undone right in the middle of the final fight between Catmare and Robin on one side, and Poison Ivy on the other.
- Lyra and Bonbon had dressed up as Bonnie and Clydesdale. In that guise, they successfully rob the Ponyville bank, leaving the teller tied up behind them. They just finish enjoying some celebratory sex when Dinky!Holmes and Ditzy!Watson show up and incapacitate them. Dinky!Holmes then rounds things off by apprehending the teller, who'd been embezzling from the bank. That chapter ends with Bonbon worriedly rubbing her abdomen after the magic is reversed.
- Fenspace: This is a possible result of handwavium accidents. The most drastic example to date is a guy who built a Trasformer using handwavium and got shot by a police sniper after being mistaken for a terrorist. He passed out in the cab, with a burst pipe leaking handwavium into the wound, and woke up with his mind now in the Transformer body. Likewise, the first catgirl was created when a con-goer in a handwavium-enhanced catgirl costume ate food contaminated with Guacamole (a strain of 'wavium specialized for bio-modification), and another guy became a cyborg when he accidentally drank a bottle of handwavium while wearing a suit of Powered Armor.
- Oversaturated World: In "Living Nightmares", Twilight performs an experimental costume-related spell that results in the creation of Darth Rarity, Sweetie Skywalker, Chief Engineer Applebloom 'Scotty' Scot, Invader Spike, and Rainbow Caboose.
Sunset: "What have we learned, Twilight?"
Twilight: "Don't take magical inspiration from Peppy the Vampire Stabber?"
Sunset: "I meant test new spells in a controlled environment, but that's probably a good rule of thumb as well."
- Monster Family: After Emma mistakenly orders monster costumes for her family from Dracula instead of the costume store she intended to call, and following a spell from Baba Yaga, each member of the family is transformed into the monster they were dressed as — Emma into a vampire, her husband Frank into Frankenstein's Monster, her son Max into a werewolf and her daughter Fay into a mummy.
- In Halloweentown II: Kalabar's Revenge, Kal plans on turning every human who dressed as a monster into that monster (and conversely to turn monsters into humans). He even has Gwen wear a horrific mask so that she would become a terrifying, hag-like goblin.
- In Hallows End, the characters become their costumes when they die.
- In Night of the Demons 3, the demonic Angela Franklin turns characters into their demon, Cat Girl, and snake-armed gorgon costumes.
- The Sorcerer's Apprentice has The Dragon Horvath turning a Chinese dancing dragon into a real dragon.
- Onibaba: The mask worn by a samurai warrior, and later one of the female protagonists, is implied to have this effect.
- The House That Dripped Blood: In "The Cloak", actor Henderson purchases a vampire's cloak to add verisimilitude to role as a vampire, only to discover he transforms into a vampire whenever he dons the cloak.
- Flossie Teacakes's magical coat may be a benign version of this — a particularly fabulous coat that she finds in her older sister's room turns out to magically transform dowdy ten-year old Flossie (when she plays at dressing as her sister) into the young woman that she dreams of being.
- In one of the Doctor Who Expanded Universe books, Forever Autumn, this happens because of some strange occult-sciency aliens wanting to harvest fear from everyone so they can leave Earth. Yes, Clarke's Third Law is in effect here.
- Magic: The Gathering: In the Ravnica tie-in novel, Agrus Kos and his angel partner, Feather, arrest a troupe of actors after a faulty "Performance Enchantment" causes the man playing a bloodthirsty Gruul war chieftain to get a little too in-character. Fortunately, nobody is injured.
- In Robert Bloch's "The Cloak" the title garment gave the guy who was wearing it vampiric urges.
- Jackrabbit Messiah: There's a brief bit where the hero (and his Helpful Hallucination) have to Journey to the Center of the Mind. While there, Jack's costume is no longer just a costume!
- Buffy the Vampire Slayer:
- Season 2, Episode 6: "Halloween". This episode is one of the fandom's favorite launch points for crossover Fan Fics in which someone (usually Xander) dressed as a character from another fandom, to the point where "YAHF" (Yet Another Halloween Fic) has entered the fandom vocabulary.
- Exploited in the Season 4 episode "Fear Itself", where the gang attend a college Halloween party and all of them dress up as someone or something that would actually be useful should history repeat itself. This time, though, it's just the Halloween decorations at the party that get brought to life.
- The same trick is pulled on a convention in the later Angel comics, turning a bunch of nerds into superheroes and villains, and turning Spike into Angel. Or, at least, Angel as Spike sees him.
- The Twilight Zone (1959) has "The Masks", where a dying millionaire forces his worthless heirs to wear masks caricaturing their worst personality traits — if they take them off before midnight, they get cut out of his will save for some fare to take the train home. At midnight, he dies, and they shed the masks... and discover their faces have taken on the shapes of the masks permanently save the good-hearted millionaire, who retains his human face. It should be noted this isn't set on Halloween, but Mardi Gras in New Orleans.
- Abed from Community is probably worth an honorable mention. In the Halloween episode "Introduction to Statistics", he dresses up as Batman, and although technically he never actually turns into Batman (despite appearances, it's not that kind of show), he commits to the part to such a degree that some of his friends start to think he actually believes it. But then, he is known for his rather unique view of reality.
- Misfits has an unusual example bordering on an inversion: One character wears a gorilla costume to a costume party. In the end it turns out that he was a gorilla with the superpower to appear human, leading to a scene in which he removes a gorilla mask to reveal a gorilla face underneath.
- Sir Arthur Conan Doyle's The Lost World: In one episode, the heroes take shelter from the rain in a castle. When they decide to change out of their wet clothes into the formal outfits they find, they become possessed by the original wearers, who were evil. Fortunately, Challenger didn't do this, leaving him free to save the day.
- My Babysitter's a Vampire: In one episode, Rory puts on an ancient magical mask that gives him the power to turn people into their costumes. Unfortunately, the mask also takes control of his mind, and starts building an army. To make matters worse, the mask can only be removed after the wearer is blasted with magical lightning — something WAY out of the league of the resident wizard, especially since his Old Master witch grandmother is out of town.
- Spooksville: The Halloween costume version is used with a boy who keeps trick-or-treaters hostage as more-or-less real versions of their costumes. The resolution hinges on one of the characters being able to use part of his costume that had been a toy but is now real.
- That's So Raven: In the Halloween episode, Raven and Chelsea use a wishing spell to win the costume contest at a Halloween party. However, a mistake during the spell casting also causes them to turn into cows. Despite becoming actual cows at the party, they get voted as having the best costumes.
- In Monte Cook's World of Darkness, all of the costumes at the Guthrie Theater in Minneapolis work this way. Once someone puts on a costume, they become that character — even when the costume is removed. The effect is apparently irreversible. The theater is popular with suicidal people; by putting on a costume, they can cease to exist and instead become someone else entirely.
- The Legend of Zelda: Majora's Mask: The Deku, Goron, Zora, and Fierce Deity masks are much more than facial accessories — they contain something of the people who died to make them, and donning them turns Link into a member of their species (for the first three) or a demigod of sorts (for the Fierce Deity mask).
- Costume Quest: This is a gameplay mechanic. You play a kid who has to rescue their sibling from evil goblins using powers channeled through their costume.
- Kid Chameleon on the Sega Genesis as the main gameplay mechanic. The eponymous Kid Chameleon gains different powers and costumes from various mask power-ups found throughout the game.
- Tales Series:
- In Tales of the Abyss, Anise can be given special dolls from other Tales or Namco games (such as Presea from Tales of Symphonia and ) which sometimes prompt Anise's end battle quote to sound nothing like anything Anise would say and sometimes end up as nonsequitors, because she's channelling the character in question. They also allow her to use their special abilities (ie, Beast for the Presea doll)
- Tales of Vesperia:
- Played with in a skit in the PS3 version, where the party unintentionally start acting like the Tales characters they're dressed as. The same costumes also let them use an arte that was used by the character it belonged to.
- This is also the primary gameplay mechanic of the Narikiri Dungeon series, where donning the costumes of different classes, monsters, or Tales characters turns you into them and allows the use of the appropriate abilities.
- In Sunless Sea, there is an island called Visage where all who visit the island must don a mask to go past the dock onto the island. Those who wear the mask take on the role of the mask, both mentally and physically. For example, those wearing the frog mask will only croak when they try to speak, someone wearing a locust mask will act like a locust, and while wearing the mask of the moon-moth it's mentioned "You briefly flicker your wings". However, once someone removes their mask they immediately become the person they were before.
- Five Nights at Freddy's 3: Purple Guy's ultimate fate, where it is revealed he suffered a grievous, painful death and became entombed in the very same suit he used to commit his crimes, his restless ghost haunting it to this day.
- Most legendary skins in Overwatch give the characters additional lines and/or change existing ones to fit the skin's theme.
- Hanzo's Lone Wolf and Okaminote skins are very good examples, as they not only replace all dragon-related lines with wolf-related ones (i.e. "See through the dragon's eyes" is changed to "See through the wolf's eyes"), but they also change the dragons that spawn from his Ultimate into wolves, complete with a chorus of howls.
- Another good example is Zenyatta's Cultist skin from the 2017 Halloween event, which turns him into a mechanical Cthulhumanoid. His voice lines are normally very tranquil and reflect his insightful and religious nature, but with this skin become darker, more menacing, and bring eldritch themes to mind — "the Iris embraces you" becomes "the Iris consumes you", "experience tranquility" becomes "experience... nothingness". Also, the three pairs of holographic arms that appear during his ultimate ability are replaced by three pairs of jointed mechanical tentacles.
- Symmetra's Dragon skin, also from the Halloween event, visually makes her resemble a half-draconic sorceress, changing her weaponry to gain more fantasy-style armor plating and moving, reptilian-looking eyes. She gains some appropriately demonic and fiery lines, and all her ability lines have been changed to do in the scientist, now referring to her Sentry Turrets as "Sentry Wards," her Teleporter as a "Teleportation Portal," and her Shield Generator as a "Shield Well."
- The Xanadu Storyverse is all about this. At a costume convention with ten thousand in attendance, costumes become real and those wearing them are changed. Mentally the transformation varies from person to person, from "Suddenly my costume is much more accurate" to "Where am I, what is this planet?", due to each costumed person technically being turned into what they perceived their costume as being — as such, two people in the same exact costume would still turn into different things based on their knowledge and interpretation of the character they had come as, how "in-character" they were, what they were thinking or doing at the moment they transformed, and so on. There is also the "clothing curse", which affected some, but not all, of the transformed people and caused any clothing they put on to transform in the closest equivalent that would be "appropriate" for their character to wearnote . Stories tend to be either furry or Welcome to the Real World.
- Overlaps with Dragged into Drag on sites like Big closet top shelf all the time.
- Ink City: Discord inflicts this upon the characters when he crashes their Halloween party. This includes several residents temporarily transforming into each other thanks to their costume choices, like Rigby becoming Trevor, and Yakko becoming his own player.
- In general, this is a favorite Halloween event for Journal Roleplay games.
- From the satirical Venezuelan blog Chigüire Bipolar's article *Boy disguises as National Bolivarian Guard and hits his mother, grandmother and doggy, both the title's boy and his sister who disguised as radical oppositor.
- TLF Travel Alerts: For Halloween 2017 they warned of a student who dressed as a circle line train in 1997 who became an example of this trope and was still running in service. Consider your costumes wisely!
- In Costume Quest the kids do this deliberately to fight monsters.
- In The Fairly OddParents! Timmy wishes for this to happen on Halloween — unfortunately for him, his wording of the wish prevents him from unwishing it. He wanted everyone's costumes to be "real and scary"... and his fairy god parents just had to dress as a "floating human janitor" and a "floating human nurse". Even worse, the popular kids were dressed as Crash Nebula villains capable of forming a doomsday device that can blow up a planet.
- The Simpsons:
- In the third segment of "Treehouse of Horror XVI", "I've Grown a Costume on Your Face," a witch curses everyone in town by making them become their costumes.
- One of the Halloween comics had this happen in messy fashion when Rod and Todd Flanders became possessed by demons, including a lethal How Do I Shot Web? when Comic Book Guy, dressed as Superman, tries to test out his X-ray vision on stuff in his pocket and sets his eyes to heat vision instead.
- In the Darkwing Duck episode "Slaves to Fashion", Tuskernini, the villainous walrus filmmaker, creates a gas that causes people to take on the personality of whatever costumed character they dressed up as. Hilarity Ensues. The gas doesn't actually affect our hero, though, because he came to the party as himself.
- Danny Phantom: In "Reality Trip", a Reality Gem transforms a trio of nerds at a comic convention. Unfortunately for Danny, they were dressed as supervillains.
- In the Rugrats episode "Curse of the Werewuff", Angelica convinces the babies that they will be transformed into their Halloween costumes.
- The TV special Witch's Night Out (1978) has a witch turn two kids and their babysitter into the monsters they're costumed as. When the adults find out and turn on her, she explains that the point of Halloween is to try out different personas and imagine your potential. The adults happily start calling out requests for one-night transformations themselves.
- Batman: The Brave and the Bold has Batman turn into a man-bat hybrid, Bronze Tiger into a tiger-human hybrid and Vulture, Fox and Shark turn into, you guessed it, subjects of Animorphism.
- Without the Halloween aspect, this was the premise of the 1980s children's animation Mr Benn. Mr. Benn (a bowler-hatted Everyman) would visit a magical costume shop, try on a costume and become that character — spaceman, cowboy, prisoner, clown...
- The Magic Key: One episode plays this trope to a T. The children are about to go to a fancy dress party when, like in every episode, they are sucked into a magical world via the Magic Key. In this one they meet a farmer whose crops are being eaten by a group of rooks, led by an anthropomorphic leader called the Rook King. When the children try to help the farmer, the Rook King turns them all into their costumes using his staff and they have to work out a plan to defeat him whilst trapped in their new forms. Once they capture him and get hold of the staff, they turn back to normal.
- Teen Titans Go!: In "Monster Squad!", the Titans decide to be the scariest trick-or-treaters in town, so Raven turns them into real monsters.