A character gets hit with a spell, Curse, or Transformation Ray, causing an instantaneous and involuntary transformation into a harmless or useless form. This is commonly some sort of animal creature (whether real or fantastic), though it can also be a plant or a lifeless object. This form will render them unable to pursue their goals, until they can revert to their usual form by some means — they may or may not lose their voice, or even their mental faculties (in which case someone else will have to seek the cure for them).
Frogs, newts and toads are so common that they have their own subtrope, Bewitched Amphibians. Other common choices include mice, chickens, pigs, and sheep.
In role-playing or video games, this is frequently a Standard Status Effect that will disable or greatly weaken most attacks and magic, but will rarely affect the victim's Hit Points or armor. People may get turned into toads, but — hot damn — those toads will be Made of Iron! A notable exception is when insects are involved, in which case the victim is not long for this world.
This is common in fiction, as it's a way for a spellcaster to defeat a foe with magic without simply killing them. It's also generally less permanent and more palatable than actual death. Often requires a hero to find the magic "cure" to turn his friend back into a person. This can be also be used to show a specific aspect of the character's personality, such as greedy persons turned into pigs, or cowards into chickens.
Occasionally in fiction a character may manage to save the day while still under this effect, sometimes through use of the animal form's abilities. This will lead to the Aesop that it's brains, not strength that's important. Or that courage is more important than size. Or that you can lay an egg and still feel like a man.
If the transformation is presented to disturb and frighten the viewer, it becomes Transformation Horror. It will then probably be a Painful Transformation.
Whether or not a Baleful Polymorph is effective against a Voluntary Shapeshifter varies, depending on whether or not it also imposes a Shapeshifter Mode Lock — otherwise the shapeshifter can just transform themselves back to normal, or at least something else. Thus, it is a subtrope of curses.
Depending on the method, clothing may be transformed as well, or it may not, resulting in Shapeshifting Excludes Clothing if the characters or audience are aware of this fact, or Empty Piles of Clothing if they are not. (In either case, naturally, when they get turned back they're going to need those clothes back...)
Polymorphing into a nonliving form is much less likely to be played for laughs and much more likely to be permanent.
Can be used as a Karmic Transformation. Characters transformed this way may also exhibit Morphic Resonance. See also Emergency Transformation, Shape Shifter Mashup and Beauty to Beast. Compare Taken for Granite (turning into a statue), Unwilling Roboticisation (turning from flesh into something mechanical). Compare Spawn Broodling, in which the "Baleful" part is turned Up to Eleven. Contrast with Hybrid Overkill Avoidance, where the subject is immune to further polymorphing because they're already supernatural. Compare Involuntary Shapeshifter.
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Anime and Manga
In Dokkoida?!, Hyacinth's henchman Pierre has the ability to morph into almost any animal when whipped. The animal is always random, and never anything useful. However, in the past (i.e. before the start of the series) he morphed into animals that were quite threatening indeed, leading to Hyacinth's status as an A-class villain.
Dragon Ball Z villain Captain Ginyu (who has the ability to switch bodies with his opponents) is defeated when he is tricked into switching bodies with an ordinary, powerless Namekian frog. When the planet he is in explodes he is transported along with everybody else to Earth, and stays on Earth, along with the frog now inhabiting his old body, until the planet is destroyed by Kid Buu. In an anime filler, he manages to switch bodies with Bulma, but is soon forced back into his frog body.
In the final saga, Majin Buu turns Vegito into a candy ball. Said candy proceeds to kick Buu's ass (while the audience' laugh theirs off). Buu, considering Vegito to be even more dangerous as what basically amounts to an absurdly powerful living bulletnote Note that reducing the surface area of an object while not reducing the force it exerts increases the pressure, hence doing more damage. Yay, physics!, decides to change him back. Now that's entertainment.
"I'm no ordinary candy! I'm a jawbreaker, the strongest candy there is!"
An All There in the Manual example in Fairy Tail: Kinana was turned into a snake ten years ago and made to fight alongside Cobra, until Marakov turned her back. She doesn't have any memories of being a snake.
Tomoe from Kamisama Kiss likes to transform an opponent into a game animal of some kind and then try to cook them alive.
In Negima!?, Negi does get turned into a chupacabra, but he gets better.
In a story of one the Mazinger Z manga versions, a race of giant, man-eater, fish-alike, humanoid Eldritch Abominations from another dimension named Chip Kamoy tried to invade Earth. They kidnapped a normal human girl and transformed her into a mermaid-like being to communicate with humans. Later they trapped The Hero Kouji Kabuto and she helped him to escape. In punishment she got executed by the Chip Kamoy.
In Nyan Koi!, Junpei will turn into a cat (which pretty much kills him, since he's allergic) if he doesn't perform one hundred good deeds for cats.
Any Witch in Ojamajo Doremi is turned into a Witch Frog whenever a human calls them a Witch. They can be changed back, but only the one who called them can pull it off. Unfortunately, most humans run away in fear when it happens, leaving many unfortunate Witches trapped in that form for the rest of their lives. It's even implied that most Witches never return to normal. Averted later on when the curse the causes the Baleful Polymorph is lifted by the one who originally cast it in the first place; it still came too late for those who died as witch Frogs.
Ash Ketchum gets turned into a Pikachu at the end of an episode of Pokémon thanks to a rather careless magic spell. Luckily for him it only lasts for a while (Unluckily for the audience we barely see him do anything in this time).
Pokemon also had Sabrina, who while suffering from Literal Split Personality turned some people into dolls with her psychic powers.
Inverted in Princess Tutu — Ahiru is actually a duck to begin with and gets turned into a human girl, but certain circumstances will cause her to revert to duck form ...
In Ruin Explorers, Ihrie turns into a rat every time she uses her magic, a curse from her old master.
Used in Sailor Moon, when Wiseman tricks Esmeraude into putting a crown on herself that would boost her powers. It turns her into a mindless dragon instead.
In Spirited Away, Chihiro's parents are turned into pigs. And in the same movie, a giant baby is turned into a hamster, and a large bird is turned into a tiny black hummingbird-thing. This trope is used a lot in Miyazaki movies, it seems.
This trope is central to the plot of the ero-mangaTentacle Lovers, wherein a young man is turned into a small, cute tentacle monster after a foreign princess botches a summoning spell. Played with by the end, wherein the Princess managed to make a new body for the protagonist, and transfers his soul into it. However, because it was designed from her memory (and the two had several Mate or Die moments), his new form was a bit more... endowed... than it used to be.
Uzumaki features some people who transform into snails, and one couple who become snake-like. This isn't too bad for the snailized people until the un-snailized people start looking for food.
In One Piece, the samurai Kin'emon's missing son Momonosuke ate an artificially created Devil Fruit that turned him into a little eastern style dragon. Whether due to his inexperience with Devil Fruit powers or problems with the man-made fruit itself, Momonosuke is stuck in dragon form.
The Dressrosa arc introduces Sugar, a member of the Doflamingo pirate crew. She has eaten the Hobby-Hobby fruit, which grants her the ability to turn people into toys and even remove people's memories of them. Though this comes with a tradeoff that she's stuck in the physical body of a ten-year-old girl. Actually, even thatdoesn't come as a disadvantage.
In Fruits Basket the story centers around an entire family cursed that they turn into animals when embraced, though luckily they keep their human minds and can still talk. But expect an awful lot of awkwardness when they turn back Though the family learned to accept and deal with the curse, they still consider the whole thing a Blessed with Suck especially if you're Hatori. (He turns into a seahorse)
In Campione! when Sun Wukong manifests on Earth, all non-magical humans in the surrounding city are transformed into monkeys. Notably, this is not out of malice but primarily because Sun Wukong desires subjects to rule over; the transformed civilians are unharmed and eventually return to normal.
In Gintama, a story arc focuses on Gintoki, Katsura, and Kondo trying to return to their original forms after they're cursed as a result of relieving themselves on a cat's grave. The former two transformed into cats, while the latter of the three inexplicably ends up as a gorilla instead (Befitting of his nickname). Despite the change, they're still able to beat up the ones responsible for capturing Kabukicho's stray cats rather easily, though in Kondo's case, it's more than justified.
Calvin was once turned into an owl by the Transmogrifier Gun, but accepted it when he realized that he wouldn't have to go to school. He was actually disappointed when the transmogrification wore off.
He once used it to turn himself into a tiger, he ended up looking like a shorter Hobbes
After the Fantastic Four defeat them, three Skrulls offer to turn into something else (and be hypnotised into forgetting their previous lives.) They are turned into cattle and put out to pasture. Which is very creepy after Fridge Logic sets in. In fact, that's not the last we ever hear of the Skrull-cows. The meat they are eventually turned into winds up giving a group of ordinary people superpowers. And cancer.
In Transfer of Power, The Authority's punishment for the superpowered monster that attacks them (depowered back into a hick) is to take him back home and change him into a flock of chickens. Just as the local bar turns out and the locals decide chickens are acceptable sexual partners. "Do you remember when heroes just used to take bad guys to jail?" (In this case, the reason they didn't is because the hick was empowered by G7. Yes, the seven wealthiest governments in the world. His jail stint would have been shorter than Paris Hilton's.)
Worse, actually: the locals are actually his brothers, who had just been complaining about a lack of anything to eat.
In the Buffy comics, Dawn has been turned into a giant (well, at least she got to stomp Tokyo and fight a giant robot version of herself), a centaur (uh, gave Xander a ride...) and a doll.
In the comic book Fables, the realm Prince Charming came from had its fair share of cursed folks being turned into all sorts of talking animals. Of course, marriage to royalty would reverse the curse. King and Queen Charming disposed of the more troublesome ones by summoning the cook...
Also, in a slight twist a rabbit named Colonel Thunderfoot is transformed into a human by the angry rabbit mother of a soldier who died after Thunderfoot sent him to battle. The terms of course were that Thunderfoot could only be turned back into a rabbit if he found a doe able to see past his appearance and love him. Judging by the end of the chapter, he is in rather bad luck on that score.
This is The Spectre's general specialty, with origins as a method of getting murder past the Comics Code Authority. Generally, the polymorph is such that the transformed person gets killed or destroyed horribly in such a way as to make ordinary murder seem pleasant... but because it wasn't a human (or, often, a living thing) getting horrifically murdered, its OK!
In some of the Witch Hazel in Little Lulu, hazel transforms Lulu into various things, such as a cat, a parrot, a monkey, a mermaid, and even a water pipe!
Before Swing with Scooter turned into an Archieclone, its seventh issue featured a story where Scooter and his friends were turned into anthropomorphic vegetables. Yes.◊
The mutant Masque of the sewer-dwelling Morlocks can alter the flesh of anyone he touches, in pretty much any way he can imagine; and he has a very twisted imagination.
Sersi of the Eternals is the Marvel Universe inspiration behind the legend of Circe, and often temporarily transforms her foes into harmless animals.
Circe the Goddess is a straight-up villain for The DCU and turns her foes into animals. This doesn't stick for Plastic Man, for obvious reasons, but does kinda turn him on.
All Fall Down: Entertaining children in hospital, the shape-shifter Phylum is permanently trapped in the form of a chimpanzee.
One Mickey Mouse comic had a witch turn Minnie into a lamb by tricking her into eating an enchanted fig.
Witch Girls has this occur several times in its comics, notably with Lucinda Nightbane turning a couple of muggers into a frog and fly, and another in which she turns a bully into a two-headed rabbit who she releases into the world to breed.
The Mighty Thor was turned into a frog on more than one occasion. One time his fellow Avengers were transformed too. Thor groaned "not again..." while Iron Man started freaking out.
In The Smurfs comic book story "The Little Tree", Lumberjack Smurf finds out that an elf's sister has been turned into an evergreen tree and spares her from being cut down.
In "Earl of Mar's Daughter", the hero's mother is a "queen o state and wealth" who is so "well skilld in magic spells" that she transformed her son into a dove so that he could fly to distant lands to "charm such maids" as the heroine. In another version, the mighty queen does this to her puny son because he wouldn't obey her.
In "The Wonderful Birch", after the hero marries the heroine, the Wicked Stepmother turns her into a reindeer and puts her own daughter in her place; a wise woman brings her child to the forest and she turns to a woman to tend it, and her husband burns her skin.
In Diaries of a Madman, Athena cursed Arachne by transforming her into a spider, in revenge for an insult.
In Shadowchasers Torment, the Doomdreamer Loreli did this to enemies, former lovers, and even to her own father, usually turning them into cats, keeping a few of them as pets simply to torment them. Nichole fell victim to this too (a "punishment" for breaking into Lorlei's room when the heroes made their final assault on the villain's HQ), but was rescued from the protagonist shortly before the spell became irreversible. (Because Lorlei was Genre Savvy enough to realize that she might accidentally fall victim to the spell herself since she used it so often, she kept a magical curse-breaker hidden in her room, where she cast it often; she was sure to lock up victims in a cage to make sure they couldn't look for it, but never counted on a rescue attempt.)
The same fate befell Loreli herself at the conclusion; she accepted it as a plea bargain to escape the death penalty and was turned into a cat before being resigned to a private cell at the prison complex. This didn't last long, as she was broken out and cured (against her will, although she didn't have much choice) in Shadowchasers Ascension by the Big Bad of that fic.
This trope is one of the key aspects of A New World, A New Way and it's sidestories. Arcues moves a vast majority of the Pokčmon and a handful of humans to Equis, and turns the selected Humans into Pokčmon. Some of the humans don't mind the change though.
Films — Animation
Disney uses this a lot. Beauty and the Beast has the Prince involuntarily transformed into the Beast by the Enchantress, along with the other servants.
In Cinderella, the mice and dog are turned into the footman and horses. Cinderella III: Twist in Time has the Stepmother steal the Fary Godmother's wand and ultimately turn Anastasia into a copy of Cinderella to steal the Prince away. While Anastasia might have been bullied into agreeing, she still seems rather upset about the whole thing.
Abu is turned into an elephant and later a wind-up monkey toy.
Jasmine's tiger is turned into a kitten.
And inverted when Jafar is turned into a genie, in an itty bitty living space.
In Alice in Wonderland, the protagonist changes size at alarming rates. While it does happen because she herself consumes various food and drinks, she usually is unaware of the exact effects of the consumption.
In The Princess and the Frog, Naveen and Tiana are both involuntarily turned into frogs. (The voodoo man promised "green" in Naveen's future ...)
In Pinocchio, the wayward boys are turned into donkeys. Bit by bit.
Brother Bear is based on this trope. Kenai is turned into a bear by the Great Spirit and his recently deceased eldest brother Sitka as punishment for attempting to avenge Sitka by killing the bear. Justified when it turns out to be the mother of a bear cub named Koda.
The movie features a slew of polymorphing potions going awry, and some of the results are much less than useful — becoming a turtle, a parrot, and a humpback whale are each pretty Baleful in their own right.
The main character, Kuzco, is turned into a llama by Yzma by means of one of these potions.
And then there's the entire palace guard, who get transformed into several different creatures, though their baleful-ness is apparently up to the individual:
Guard: Uh... I've been turned into a cow... can I go home? Yzma: You're excused. Anyone else? The rest of the troops: Nah, we're good!
And of course Yzma gets her comeuppance when one of the final potions is used on her. And she turns into a fluffy little kitten. Cue Kuzco taunting her until he gets scratched.
evil empress Bavmorda transforms all of an army into pigs this way. The pig transformation was also used as a temporary status effect in the NES RPG based on the movie.
The sorceress Fin Raziel is also subjected to this treatment, though Bavmorda turns her into a possum, not a pig. And then Willow himself transforms her into... a bunch of other animals, with nary a pause in between. She (finally) gets better.
Goat!Fin Raziel: Maad Maartigan... Madmartigan: What the Hell happened to you?
In Time Bandits, the Source of All Evil turns one of the dwarves into a pig.
The movie Russell is about a man who gets turned into a koala.
The film Ladyhawke has a double case of this, orchestrated by an evil priest. Two lovers are cursed so that the man, Etienne Navarre, becomes a wolf by night, and the woman, Isabeau, becomes a hawk by day. They can only both be human at exact sunrise and sunset, but they can never touch.
In Hocus Pocus, young Binks is turned into a black cat by the three sister witches, and is doomed to live forever with his guilt.
The hero is promised safe transportation, food, and lodging by a witch. She turns him into a mouse and puts him in a cage with some cheese. As noted in the example in the Literature section, there is a practical reason for the transformation, rather than it just being a curse — the witch didn't want Tristan to take up a lot of space and eat a lot of food.
Also, Lady Una is turned into a bird and back by the same witch. She seems rather pissed about it.
Earlier, the villain changes a farmboy into a goat to help pull her carriage. Later, she changes him into a young woman and the (real) goat into a man as a subterfuge. The drawback is that their voices don't change.
In ''Sinbad' a sorcerer turns Sinbad's friend into a dog.
This is used as a disturbing visual element in Black Swan, where the protagonist imagines herself morphing into an actual black swan as she struggles psychologically with her role in the ballet. Unless it's really happening...
In High School Musical 2, the "Humuhumunukunukuapua'a" skit is about a lonely Hawaiian princess who seeks to break the spell on a prince who's been turned into a fish.
In the Turkish film Tatlı Cadının Maceraları (Adventures of the Sweet Witch) (based on Bewitched), a magical evil woman promptly transforms a man into a goldfish on a frying pan when he is unresponsive to her advances. He is later rescued by his magical wife.
The evil Djinn in Wishmaster does this many times to his victims, with multiple variants. He changes people into trees, brick walls, mannequins, glass doors, crocodiles, a pimple on someone's ass, and many other unpleasantries.
Maleficent turns the raven Diaval into a man to save him from being beaten to death. When he later pledges his service to her, she changes him into whatever form best suits her needs.
Maleficent: I need a horse...
Very common in Arabian Nights, where it is typically employed by sorceresses who are either hit upon by men they do not like, or for the purposes of punishing an erstwhile lover they are tired of.
Example of both kinds are found in the story of King Beder. King Beder is first turned into a bird by Princess Giauhara when he tries to kiss her hand. He is later rescued by another benevolent sorceress queen, but then reaches the city of the formidable Queen Labe. She is so much into this trope that the first thing Beder notices on entering her kingdom is the abnormally large number of donkeys, mules and horses on the streets, who, he later learns, were all her former human lovers whom she had transformed into animals after she tired of them. Beder himself escapes her clutches when he first meets her, by transforming her into a mule with assistance from a magician friend. However, Labe is rescued by her mother, and quickly has her revenge by changing Beder into a "foul bird".
Another extreme example is found in the Tale of the Younk King of the Black Isles, where the king in the title is transformed into a living sculpture-he is stone from neck downwards- by his adulterous wife as punishment for harming her lover. The queen is not content with merely transforming the king her husband, and goes ahead and makes a display of her magical powers to him by transforming all the inhabitants of his kingdom into fish, color coded by their religion. This whole transfiguration explosion is later discovered when a fisherman tries to catch these fish and finds them to be rather unusually jumpy.
Taken to an extreme in the story of The Merchant and The Djinn - the titular merchant finds himself having incurred the murderous wrath of the titular Djinn, but is saved at the last moment by the intervention of three completely unrelated travelers who happened to be in that stretch of desert at the time, all of whom are carting around various animals that all happen to be their wives/brothers/relatives who have had bad/foolish experiences with magic and were put under a spell - in something of a parody of this idea. What follows are various stories within stories explaining how each of them suffered this fate, and The Djinn is so amazed by having heard them that he agrees to let the merchant go in exchange for the experience.
And in his The Magic Finger this is the main character's special ability, although it so horrifies her that she never uses it unless she's really annoyed with someone.
Violet Beauregarde's karmic fate in Charlie and the Chocolate Factory is a transformation into a giant blueberry, with only her head, hands, and feet showing that she was once human. (This is played up in the 2005 film and 2013 stage musical adaptations, in which her parent figure in each has Skewed Priorities with regards to their concerns for her — in the former, it's that she won't be able to "compete", and the latter, that she can't be a starlet in this form.) At the end of the novel, after all the juice is squeezed out of her, she's Not Quite Back to Normal, as her skin and hair are still blue.
In The Magic of Oz, a young boy learns to use a very dangerous magic word ("Pyrzqxgl", hard to use because very few can pronounce it) which can turn anything into anything. He learns to pronounce it, and becomes an Unwitting Pawn of the villainous Nome King, who convinces him to use it to wreck havoc in Oz. Naturally, Ozma's protectors try to stop him, until in one scene, he panics and says it dozens of times, transforming nearly the entire cast into various animals - including the Nome King too, who makes the mistake of making him angry. Eventually, the Wizard himself is able to use the word and turn it against them, then trick them into drinking the Water of Oblivion to make them forget the word and return them to a "blank slate". (Which, in the Nome King's case, only stops his evil ways for a short time...)
In the novels, it's stated that Granny Weatherwax doesn't do this. Instead, she prefers to make people think they're frogs, which takes much less magic, is slightly less cruel, and is a lot more entertaining. The Discworld does, however, contain a few instances of turning people into animals and lots of threatening to turn people into animals. They usually, but not always, get better.
He also turns a particularly annoying complainer into a frog, albeit briefly, in Soul Music.
Going Postal: "Oh, PLEASE sue the University! We've got PONDS full of people who tried to sue the University!"
In Sourcery, a University wizard in service to Coin the Sourcerer transforms Lord Vetinari into a small lizard, one of the few times anyone's gotten the better of him.
In Witches Abroad, Lilith, the quintessential "good witch" gone bad, revisits the Cinderella tale by turning animals into humans and vice versa. When upset at some coachmen getting drunk, she turns them into cockroaches — and steps on them.
The Librarian of Unseen University is a subversion: he's accidentally turned into an orangutan near the beginning of The Light Fantastic, but he prefers it so much (it's easier to fetch books from on high, for example) he refuses to be transformed back. His morphic field seems to have been permanently affected, as any other time he's transformed, he retains his red-orange orangutan fur. In later novels, his orangutan strength helps save the day.
And in Equal Rites one silly boy was turned into the "more fitting" form of a piglet.
In A Hat Full of Sky, Tiffany Aching temporarily gains the ability to transform an arrogant would-be wizard into a frog, though her magic isn't yet powerful enough to violate the conservation of mass, thus necessitating making a giant magical bubble of all the leftover matter from his body next to the frog, which is more horrifying in many ways than the frog-transformation itself.
The Tiffany books also have the Toad, who was once a lawyer who tried to represent a girl in a Frivolous Lawsuit on a fairy godmother. It was the judge applauding that really got to him, though.
A witch turns Tristran into a dormouse to carry him in her cart. In the novel, it's made clear that this isn't actually meant as a curse; it's done for practicality: Tristan takes up a lot less room this way after him arranging for food, bedding and travel. It's also implied that the spell turns you into the animal you are most like. The witch also turns Tristran back once she's given him a ride. OTOH, she does find it amusing.
The witch earlier turned Tristran's mother into a bird as a punishment.
The Dresden Files not only consciously avoids using this trope, but the author has actually come up with a plausible reason why most "good" wizards have outlawed the practice.
Ursula K. Le Guin's Earthsea makes a spell to shift another person involuntarily rather difficult, and making shifting yourself perfectly easy, but running a very real risk of forgetting how... and why... to shift out of the other form.
This happens a number of times in Harry Potter, usually played for laughs. Justified in that one of the classes is Transfiguration, and a lot of students have bad aim. One example is Draco Malfoy, the Amazing Bouncing Ferret, in Harry Potter and the Goblet of Fire. "Quidditch Through The Ages" also mentions that after one early match, they had to specifically come up with a rule prohibiting Transfiguring the Keeper into a polecat, although given that the use of several weapons and releasing a swarm of vampire bats were also banned after that match, whether this was intended to prevent the enemy from remaining on their broom or to increase their own team's ability to drop on other players and savage them remains a mystery for the ages.
In The Belgariad, Polgara uses this twice during the course of the series. She permanently transforms Queen Salmissra into a huge serpent in the original books. (Salmissra comes to appreciate the benefits of the change, and does not want to be returned to her previous form). In the prequel Polgara The Sorceress, she temporarily transforms one of the Cherek kings into a man-sized frog because she thinks a regular Dope Slap won't be enough to get the message across.
Mentioned in The Malloreon, when Beldin and Belgarath are talking to a sorcerer who hasn't learned the rules. Beldin discourages it, on the grounds that having one annoying person is less tiresome than having a hundred aggravating frogs.
In Ella Enchanted, Lucinda, a fairy of the gift-bestowing kind, doesn't think through the consequences of her 'gifts'. One of her favourites is turning people into squirrels, and she believes she's doing them a favour until she spends a week as a squirrel herself.
In one early short story from The Witcher saga by Andrzej Sapkowski, a young knight named Dani is under the spell that turns him into a giant hedgehog at day, and Geralt helps him remove it — the whole story is rather gleeful deconstruction of the classic "Beauty and the Beast" plot. Of course, Dani is a Nilfgaardian prince who later went to become The Emperor Emhyr var Emreis, so it's a hell of a Chekhov's Gun...
The actual D&D spell has a notable use in RA Salvatore's Exile. As noted under Tabletop Games, the spell gradually takes over the object's mind, which in story terms makes for all kinds of tragedy.
Ironically enough the novel Polymorph, which is about a literal "baleful polymorph" (e.g. an evil creature which can assume any form) contains no examples of this trope, since it cannot transform others.
Tom Holt's work both plays this straight and subverts it.
In Falling Sideways many, many characters get turned into frogs. Or made to think they're frogs. Or made to seem like frogs to others. Or various combinations. Sometimes frogs get turned into people, which, for the powerful, super-intelligent alien frogs in the story actually pretty much counts as this trope. There's a lot of frogs.
In the J.W. Wells & Co. trilogy, the standard punishment for betraying the firm is being turned into office supplies. You retain some measure of sapience.
It features a spontaneous example when Woraug turns into a toad, having lost the privilege of being a dragon by not acting dragon-like enough.
In in the later books, it's mentioned that there are countless ways a careless person could be cursed and turned into a flower or animal or rock or something in the Enchanted Forest. When Mendabar and Cimorene get married and they're clearing out a meadow for the occasion, they find and disenchant several kings and princesses. In Calling on Dragons, Cimorene mentions how you have to be careful in the Enchanted Forest, because you could sit or walk on someone important without knowing it. And while it's more of a spell transfer than an actual transformation, we also get the annoying fellow with the long name getting turned into a sky blue, twelve-foot-tall donkey, floating above the ground and with giant wings.
Kingdoms of Light's Six-Man Band consists of a mage's pets (three cats, a dog, a snake, and a canary), turned into humans by the mage's dying spell. In the end, they are captured by the evil Munderucu and turned back into animals — except that due to character growth, they not only remained sentient, but they became great cats, a huge wolf, a firebird, and a 40-foot python. Oops.
"Evil" Magician Trent of the Xanth series can transform anything into anything. When he was ousted, rumors spread that he turned his enemies into fish and left them to suffocate on dry land. Trent explains that he did turn some into fish but only in rivers or other bodies of water.
Rabadash, the Calormene prince, gets temporarily turned into a donkey, and is warned that it will happen again if he moves more than 10 miles away from the temple of Tashbaan.
Subverted (unintentionally?) with Eustace Scrubb, who gets turned into a dragon as a punishment. While being a dragon seems awesome, he couldn't talk (and could barely write), couldn't fit on the boat to continue the group's quest (so would have had to spend the rest of his life alone on the island), and was wearing an armlet that was perfectly-sized for his human form but was digging into his foreleg and causing him constant pain as a dragon. And it has the intended result as well, turning him into a much better person in the end.
There's also the unpleasant schoolchildren towards the end of Prince Caspian, who get turned into pigs.
Rosemary and Rue begins with Toby being turned into a fish by the Unseelie kidnappers she was tracking, and left in a koi pond at the Golden Gate Park Japanese Garden. It takes fourteen years for the spell to wear off.
Secret Histories: Wild witch Molly Metcalf admits to once turning a fox hunting party into foxes for a day, feeling it would give the hunters some perspective.
More than a few Goosebumps books had this as a problem the kid-protagonist had to face, caused either through magic or technology.
In No Such Thing as a Witch, Nora and Todd find out that if four pieces of their neighbor's magic fudge are eaten together, it can turn you into whatever animal you're thinking of at the time. The first time this happens, it's to Todd and no one was expecting it. Towards the end of the book, Nora deliberately uses it to turn herself into a mouse to sneak into the neighbor's apartment. Todd also turns into a cat a few more times, with one of those times being nearly in front of a health inspector!
Treasure at the Heart of the Tanglewood is a bit confusing regarding this trope. It's made clear early on that there's something off about the knights who seek the Tanglewood's treasure, and it's eventually revealed that they're all animals, turned human by a sorceress and forced to serve her. Only that's a lie: they were humans the villain turned into animals, and the sorceress turned them human again, and then the villain turned them into animals again.
The first of the Endless Quest pick-a-path books, Dungeon of Dread, was a surprisingly-grim adventure in a dungeon where all the monsters were created by an evil wizard casting this spell on enemies or innocent bystanders. There's nothing you can do to restore the victims, but the villain gets Hoist by His Own Petard, succumbing to this trope in turn, in the best ending.
The Evil Sorcerer from Dungeon of Dread, the first ever pick-a-path adventure book to be based on the D&D game, stocked his lair by transforming innocent townsfolk into various Big Creepy-Crawlies and other monsters.
Discussed in The Lord of the Rings. Characters believe that the wizard Gandalf might turn Sam into a newt, or Mr. Butterbur into a block of wood. Gandalf might not even have this ability. Sam and Butterbur behave well enough that no transformation is necessary.
In the ''Mercy Thompson verse, sufficiently powerful Alphas are able to force members of their pack to change to werewolf form. This can be handy for temporarily stopping them in their tracks, as the change generally takes 15+ minutes.
In Mogworld, there's a bunny morph spell that Jim eventually buys. According to Jim, "It's a combat control strategy that also happens to be incredibly hilarious." It gets deconstructed when he explains that polymorphed rabbits are indestructible, because if you can turn any foe regardless of size, into a small harmless rabbit and instantly kill it there, then there would be no point in buying any other spells.
In The Cats Of Tanglewood Forest (and the children's picture book it's based on, A Circle Of Cats), the titular cats do this as a way of saving the main character, Lillian Kindred, who had been bitten by a snake, so they turn her into something that's not dying, a kitten. As soon as Lillian wakes up, she sets off to get the spell reversed (as she prefers to be a girl), only the cats are in hiding now as their leader, The Father of Cats, disapproves of them using their magic in such a way.
In Andre Norton's Dread Companion, Kilda finds that eating the food of the land slowly turns her toward a creature of it, and Oomart too. Fortunately, she has human food, which can turn you back.
In the short story Lady Into Fox, a dainty elegant woman is turned into a talking fox, and very gradually becomes one mentally. The woman who always wore napkins and fancy etiquette, was now eating live rabbits in the living room. It was never explained why she transformed. But it's assumed that some karmic celestial intervention or God himself was punishing her husband for being a fox hunter.
Froggy from The Land of Stories is a human that turned into a large frog by a wish. He's actually the missing Charming prince.
In Susan Dexter's The True Knight, the queen's only son was turned to a swan. Wren and her master were forcibly recruited to retrieve him.
In one Rainbow Magic book, some goblins get turned into goldfish.
Hundreds of victims of this effect make up the supporting case of Too Many Curses. They're all very much disappointed when the death of the wizard who transformed them fails to negate this trope.
Murderess features a race of people known as the Moonfolk, or Lavricenote Rhymes with "grease". They are infertile, and one becomes one of them by transforming under very specific conditions, and it’s implied that it’s not a good thing. Lu almost becomes one herself before ‘Hat Lad’ points it out to her.
The second book in Betsy Hanes' Bone Chillers series of children's horror novels, "Little Pet Shop of Horrors," dealt with a girl who was transformed into a dog, to be sold by a pet shop. Unlike some fictional transformations, her clothes don't come along for the ride, which creates some momentary awkwardness when she regains her true form.
In Sabina Kane: Red-Headed Stepchild the untrained Sabina Kane attempts to cast a spell to banish the demon Giguhl back to his home plane, and accidentally traps him in the form of a hairless cat instead.
In various episodes, cousin Serena transforms Darren into a lamb, an ape and a statue. She is also shown as having transformed her erstwhile lovers into a crow and the Loch Ness monster. In one particularly extreme case, she transforms a man into a bed warmer and forget to transform him back for hundreds of years, leading up to the bed warmer being put up as an antique in a museum.
In an episode, Samantha turns a chimpanzee into a man, then back into a chimpanzee, then back into a man, and then finally back again into a chimpanzee. In another episode, she transforms a detective who seems to have discovered her magical abilities into a parrot, to convince him of how powerful she really is.
In The10th Kingdom, the prince is turned into a dog almost from the beginning of the story but manages to escape and get help. He is helpless throughout most of the story but he does help the heroes when he can.
The witch Amy Madison turns Buffy into a rat with a spell. Later, Amy turns herself into a rat to escape burnage at a stake... and can't turn back. It's also possible she was trying to turn the angry mob that had kidnapped her into rats rather than herself and just suffered a Magic Misfire due to her being tied up and thus unable to properly aim the spell. Then there's that little spell at the end of the season... Amy does get restored twice but the first time, Willow doesn't realize she restored Amy and accidentally changes her back into a rat.
In the fourth season, Ethan breezes back into town for a little more fun, which results in Giles being turned into a Fyarl demon.
One episode of Hercules: The Legendary Journeys uses a magic Bow and arrow belonging to Artemis to turn Herc into a pig for most of the episode, while Iolaus and Autolycus scramble to get him restored.
In Pushing Daisies, the children of Coeur d'Coeurs are terrified of aunts Lily and Vivian because they are reputed to turn unwary children into birds. That the aunts have taught at least one of their pet parrots to say "Help! She turned me into a bird!" may have contributed to the rumor.
In the very first episode of Beetleborgs Flabber turns the kids into rats by mistake.
It's a semi-recurring thing in Power Rangers for villains to nab innocent bystanders and turn them into the Monster of the Week. I can't think of a single time the Rangers spared any thoughts for the civilian's safety; they just made the monster go boom as usual and the person would be back to normal. Either that, or the MOTW would just as often transform civilians into whatevers for the scheme of the week, which is dealt with the same way.
The episode "Psychic Avengers" ends with the family turned into chimpanzees and Buck turned into a human by a gypsy's curse after a scam. The end credits to that episode even show Al and Peg in chimp form. Though granted they don't seem to care...
Peggy: Oh well, I guess we're monkeys. (continues watching TV)
The episode "Field Of Screams" has a subplot involving this, Bud, Buck, and the new bug powder Kelly advertised called "Springtime in Baghdad". The transformations weren't shown on-screen, but what Buck and Bud end up as show. Buck was turned into a different breed of dog, then a turkey. Bud, on the other hand, grew breasts from the exposure to it. By the episode's end, they had long, floppy ears. Doesn't it make you think what "Springtime in Baghdad" is made of?
Buck:(as a turkey) I sure hope this crap wears off before Thanksgiving.
Salem from Sabrina the Teenage Witch is changed into a cat for one hundred years as punishment for trying to take over the world. This punishment is fairly standard, as other characters suffer or nearly suffer similar fates. (In one episode, an old member of Salem's gang who's had his sentence commuted visits, and he's still just getting the hang of being human again.)
The Nickelodeon sitcom 100 Deeds For Eddie McDowd is about a bully who is transformed into a dog by a mysterious drifter and must perform 100 good deeds in order to turn back.
Happens now and again in Charmed. The sisters have both turned people into animals and been turned into other creatures themselves. Usually this is because a spell backfires or has unforeseen effects, but sometimes it's deliberate.
In an episode of Merlin Morgana transforms Guinevere into a deer.
Pixelface: In "The Ugly Truth", Alexia is transformed into a yeti by a magical beauty cream.
In MythQuest, Cleo takes the place of Blodeuwedd after Blodeuwedd kills her husband. As punishment, she is turned into an owl.
Myths & Religion
Nearly every mythological tradition has examples of the gods turning some unfortunate, or sometimes favoured, human into an animal, demon, angel, plant, or mineral; either permanently or temporarily. Sometimes, even the gods themselves are affected, usually as a punishment inflicted by a more powerful or Trickster deity. This is particularly common in Greco-Roman mythology.
Occurred with considerable frequency in Celtic Mythology, to the point that it's actually difficult to find stories that don't feature at least one instance of it. The Children of Lir were turned into swans, a Welsh king got turned into a boar, Gwydion and Gilfaethwy were stuck spending three years as a breeding pair of animals that changed every year, Oisin's mother was changed into a doe, and so on.
While the cause for the ability varies between versions, the story of King Midas has his touch act like this, turning anything touched into a gold statue. Very unfortunate when his daughter went to hug him. Fortunately for him, not only is this power removed, but the victims were restored.
Named after the 4th-level baleful polymorphspell, which turns involuntary targets into small, weak animals and can make them lose their minds. Turning them into something that would kill them (a non-lunged fish on land, or a non-flying animal in a situation where only a flying creature has a reasonable chance of survival) makes the spell easier to resist, as though the target instinctively knows what he's being turned into and that the situation is even worse. Though the duration is permanent, the subject gets a second save to retain their mental faculties and their special powers.
The Book of Vile Darkness has a magic item that gets around this, as it allows single aspects to be changed (also applying a rule that if a creature becomes unfeasible it instantly dies); thus, a lethal change can be made through several otherwise harmless additions, such as giving a flying creature several dozen additional wings.
A particularly nightmarish variant of this is a staple of the daemons and sorcerers of Tzeentch. The demon gods grant gifts, usually in the form of mutations. Once you gain enough, there are two options. The first is a good one: badass daemon prince. The second is insanity, many eyes, and general fun and games. You live off grubs and act as cannon fodder. Fun. A common psychic power for Chaos Sorcerers in 40k, the ironically titled "Gift of Chaos", lets them immediately transform anyone, friend or foe, into a Chaos Spawn. Various editions of fantasy have also included various Chaos Magic spells that transform the victim into Chaos Spawn — some Tzeentchian spells instead allow the warlock to turn their victim into a Horror of Tzeentch.
Of course, the Orks aren't always that much better, given that their stronger Shamans or Weirdboyz have a nasty habit of turning people into Squigs (little bouncy things that are mostly Fungus and Teeth)
In the Warhammer expansion, Storm of Magic, miscasting while standing atop an Arcane Fulcrum can result in a multitude of destructive and/or amusing effects, one of which turns all wizards on the table into frogs. There's also a Bretonian Cataclysm spell that can do the same thing.
The Skaven have a spell known as "the Dreaded Thirteenth Spell", castable only by their strongest units (Grey Seers of 4th-level wizardry and Vermin Lords). If it hits, an entire unit of the enemy is turned into Skaven.
Exalted has Pattern Spider Touch, from the Charcoal March of Spiders Style. It allows a Sidereal to fundamentally alter their opponent in some interesting way. Typically, it's used to punch people in the face and turn them into ducks.
Witch Girls allows characters to do this with the Alteration-class spells of Animalize Human or Monsterize Human.
Super Dungeon Explore has an expansion set Von Drakk Manor including happy looking witches with the ability to turn heroes engaged in combat into Miserable Toads. Far from Miserable, they acquire several defensive abilities and a knack for stealing potions and healing from their foes. They are even reverted with a kiss from a friendly model.
In John Milton's Comus, the Attendent Spirit speaks of how Circe did this, and Comus after her.
(For most do taste through fond intemperate thirst), Soon as the potion works, their human count'nance, The express resemblance of the gods, is changed Into some brutish form of wolf or bear, Or ounce or tiger, hog, or bearded goat, All other parts remaining as they were. And they, so perfect is their misery, Not once perceive their foul disfigurement, But boast themselves more comely than before, And all their friends and native home forget, To roll with pleasure in a sensual sty.
In Richard Wagner's Lohengrin, this is what actually happened to Elsa of Brabant's brother, Duke-Child Gottfried, who was cursed by the siblings's Evil Aunt Ortrud. She and her husband Telramund falsely accuse Elsa of murdering him, which prompts the titular Lohengrin to step in her defense. It turns out that the swan that drove Lohengrin to the bank was the cursed Gottfried, turned into a swan; Lohengrin prays to God and manages to undo the curse, then elects him as the official Duke before taking off.
A rare non-animal or object instance of this occured in the Fairly OddParents sequence in Jimmy Neutron's Nicktoon Blast, when Cosmo briefly turns Ooblar into a Yolkian Elvis, complete with his personality and mannerisms.
Kid Icarus probably did this first by having monsters that can turn you into a mobile eggplant.
The third game, Kid Icarus: Uprising, introduces Tempura. In addition to making you unable to attack, it also tires you out more easily, and if a Tempura Wizard is present, it will try to eat you for a One-Hit Kill.
Final Fantasy games have Pig and Toad transformations. The Pig effect (at least in Final Fantasy IV) does disable all spells... except for Pig. (Which makes sense; otherwise, it's just another Silence with a different curative item.) The Toad effect greatly reduces Attack and Defense and disables all spells except for Toad.
Casting Toad on your own party helps you pass a couple of obstacles in Final Fantasy III.
In Final Fantasy I the group of bats found in the Chaos Shrine are actually cursed warriors from Lufenia, who explain to the heroes how to travel back into the past and end the time loop once the Four Fiends are defeated.
Final Fantasy IV begins with Cecil attacking the village of Mysidia, slaughtering townspeople, and taking their Crystal. When he returns later on, properly contrite, the villagers haven't forgiven him. Unfortunately, Mysidia is the Village of Magic. He gets polymorphed if he talks to the wrong villagers. (The way the spells work means that talking to them again undoes it.)
The Moogle status in Final Fantasy Adventure works similarly and also appears in the sequel, Secret of Mana. This status disables most actions and reduces defense to 0, which means you can easily be killed in one hit by late-game enemies in both games.
Final Fantasy VI had Imp form, which while it didn't reduce your hitpoints or the strength of conventional attacks, it did make it impossible for you to use magic or special character powers. It was more of an annoyance than threat as by the time in the game when enemies start throwing it around you will have many ways to undo the transformation but need a full turn to do it after which you might get Imped again.
The Imp example is subverted in that there is a series of Imp-specific equipment that can actually allow an Imped character to administer a beatdown.
In the early versions of the game a certain Good Bad Bug allowed Gau to Rage while Imped. And a certain other Good Bad Bug allowed him to equip a weapon. An fully decked-out Imp Gau was quite a Game Breaker, although it took up one of your Relic slots.
Cid in Final Fantasy IX is transformed into an oglop (a type of verminous insect) as a punishment for being unfaithful to his wife. Dr Tot claims to have discovered a cure for his condition in an old book... which, when administered, turns Cid into a frog instead.
In Final Fantasy Tactics, a character whose Bravery goes below 10 becomes a literal chicken. The best way to do this is with Beowulf's aptly named Chicken attack, which reduces a target's bravery by 50. Chickens automatically run away from the action each turn, gaining 1 bravery point until they become human again, and their defense drops drastically.
There's also Reis, a young woman who was transformed into a dragon after Taking the Bullet for her beloved Beowulf. You can recruit her and change her back, though.
Additionally, this is useful in the Bonus Dungeon, where treasures are controlled by a Randomly Drops statistic which isn't actually random but rather linked to your Brave stat. The unit that has the highest chance of finding the treasure? Someone who's been chicken'd.
A good chunk of time in Final Fantasy: The 4 Heroes of Light is spent dealing with this. First, Aire gets turned into a cat by some cursed treasure and has to go through several misadventures, teaming up with Brandt and going to Arbor in search of a cure... only for Brandt to be turned into a human topiary because The Fair Folk don't like humans. And the mouse sage you meet in Arbor who helps? He is also one—the Fairy Queen made him a mouse as punishment for accidentally releasing Belephegor.
The Ghosts N Goblins series traditionally includes enemies that can transform you into something helpless for several seconds. Over the years the forms have included frogs, babies, bees, old men, and young womenyoung women.
Each game in the Heretic / Hexen series has a polymorph item. In Heretic, using the 'morph ovum' (an egg) would temporarily turn an enemy into a chicken. The chicken would then attack you, ineffectively. In multiplayer, being hit with this item would reduce your health to 10 and render armor useless. Your only defense is to run; you are harder to hit due to your small size as a chicken, and the effect will wear off in 30 seconds.
Hexen had the Porkalator, turning enemies into pigs. Certain traps in the game also could turn you into a pig, or by having this item reflected back on you. Some secret passages could only be navigated while in pig form, meaning that transformation is necessary to see all parts of some levels.
Hexen 2 had the Seal of the Ovinomancer, which turned most monsters into sheep (incredibly tough sheep).
In Heretic 2 the morph ovum is back, but this time has a chance of turning an enemy (in PVP at least) into a giant chicken with 999 hit points and a deadly attack. This would be a deadly problem if it weren't for the fact that you can hit him with another blast to turn him back into the less dangerous human form.
In Dungeon Keeper a spell is available that turns creatures into chickens.
Deadlocked had a weapon mod that could be attached to any weapon you had. So you could use it on your bomb launcher, and turn an entire room-full of enemies into various livestock (which includes pigs, even flying ones) all at once.
Fully upgraded, many of these weapons turn the resulting animals into ''living bombs''.
Super Mario RPG has two such effects: Characters can be turned into scarecrows that cannot attack or use items (but can still cast spells) or into mushrooms that can take no actions but slowly recover health (albeit generally not quickly enough to compensate for the damage you take in the meantime).
This is a tradition of the Warcraft series, with the most popular animal being the sheep. In Warcraft III, using Polymorph on a flying creature (such as a dragon) would turn it into a flying sheep with little stubby bat wings. The Shadow Hunter's "Hex" ability was a hero unit version that turned the target into a randomly selected critter (with different options available for ground, air, amphibious and waterbound foes). Both are temporary and can be dispelled. The lethal variety is relegated to the Goblin Alchemist hero, whose ultimate spell turns the target into gold, thus killing it and adding its value to the player's cashier.
Warcraft II played this trope straight; the Polymorph spell permanently and irrevocably turns the target into a sheep or other creature (based on the map tileset—a seal on an icepack, for example). These creatures do not retain any of the hit points or abilities of the original unit, and can no longer be controlled by any of the players... virtually making it a One-Hit Kill.
The card game Hearthstone continues this usage with the "Polymorph" card that instantly converts one of your enemy's cards into a sheep you can kill with even the weakest attack card.
In World of Warcraft, a standard instance tactic is to have the mage (if present) turn one of the mobs into a sheep to keep them out of battle till struck. Plus, Elite Troll mobs of the magic-using type often turn high-threat PCs into frogs for a short period.
Mages can also turn mobs into Pigs and Turtles, and with the new expansion, Cats, Snakes, Penguins, and Polar Bear Cubs.
Shamans have the spell Hex which turns the target into a frog for a short time. Unlike mages, they don't have a variety of forms to choose from but the hexxed target can also take some damage without transforming.
It's worth noting that these effects are all quite pointless on druids, who can break the effects by willfully polymorphing themselves into something else.
Probably best showcased in the TV spot — in French only — which featured Jean-Claude Van Damme explaining what he liked best about playing ''World of Warcraft'. The French word for sheep is "mouton," in case you were curious.
The Satyr Zenn Foulhoof gives you a quest to kill various animals for him, which pisses the Nightelves off to no end, who in turn want you to seek redemption by punishing him, by giving him a fruit that turns him into a frog.
In Lords Of Magic, the Chaos Mage had the spell Polymorph Self, which turned units (not necessarily the Mage herself) into an elephant or a lion. And then there was Polymorph Other, which would turn the target into a goat, chicken, or goose.
In NetHack it is possible to transform into almost any monster in the game (sometimes unexpectedly). Without a Ring of Polymorph Control, you have virtually no control over which monster, though — you could wind up a rat (with about five hit points, and all your human clothes and items scattered around you), a dragon (with all your human clothes and armor scattered around you, possibly in pieces), or anything in-between. But at least as a dragon you can fly and blast your enemies with variousBreath Weapons, or (if you're female) lay eggs which hatch into tame baby dragons!
A boss in Shin Megami Tensei III: Nocturne has an attack called Bael's Bane, a Curse attack with 100% accuracy that turns the afflicted into a fly. All their stats are dramatically lowered, their magic spells are reduced to a quarter-strength and worst of all, they become weak to Expel attacks (which the boss uses with alarming regularity). There's no way of curing this until the battle is over. Well, outside of death which is not an option for the hero. Your only hope of survival is to field a team that is immune to Curse attacks.
Also in the Digital Devil Saga series there is a boss called Bat, whose Atma form is the Mayan bat god Camazotz, that from the second fight on would use a spell called Curse of Zotzilaha, which turns characters into bats. The only differences are that your characters become weak to Force, rather than Expel (and of course, Camazotz abuses Force attacks), and there's no way to avoid it (it does wear off after a few turns, though). Thankfully, in Digital Devil Saga you do NOT get an instant game over if the leader is killed...
Age of Mythology includes a chapter based on Odysseus's experience at Aeaea, with Circe turning Arkantos and Ajax into boars. They must then gore villagers (the much stronger guards are apparently not hungry) to protect Odysseus and his men until such time as they can be un-piggified. Also, the cheat code "Goatunheim" turns all units into goats.
In Justice League Heroes, one of Zatana's spells turns enemies into rabbits. They retain their status as enemies, leading to such scenes as Superman frying said rabbits with heatvision.
In The Legend of Zelda: A Link to the Past, touching a certain dungeon enemy will turn Link into a giant pink bunny - still wearing Link's clothes, but unable to use any weapons or items. (Wears off after a minute, but all you can do is run, until then.)
The same form Link is turned into when he goes into the Dark World without the Moon Pearl.
In the same game, use of the Quake Medallion will turn all enemies on screen into blobs.
The Triforce of Power transforms people into creatures reflecting what is in their hearts, for example, the evil and greedy Ganon(dorf) was turned into a anthropomorphic wild boar.
Majora's Mask begins with Link transformed into a Deku Scrub (essentially a walking plant) by the Skull Kid. One of the first tasks you are given is to find some way to reverse this (and once you do, you can freely transform by donning a mask, though this causes Link to scream in apparent pain).
In the same game, Kafei is transformed into a child.
Pretty much anything touched by the Twilight becomes polymorphed into a monstrous version of itself. Then there's the Shadow Beasts, which are actually the peaceful Twili people, changed by Zant, and of course Midna, the namesake princess, who was cursed with her implike form also by Zant.
Although there was that one line in Kakariko: "Those two shadow beasts came and carried her off! And when we went to rescue her, there were three!!"
In one of the Oracle games, a later mini-boss has the ability to temporarily turn Link into a monkey, which greatly slows him down and leaves him unable to use weapons.
Also in the oracle games you can get rings that turn you into monsters, such as a Like-like and Octorok.
Phantom Hourglass has an inversion, as the Ocean King, normally a great whale, has his power sapped by Bellum and spends most of the game as old man Oshus.
In The Legend of Zelda: Link's Awakening Tarin is turned into an anthropomorphic raccoon, though it seemed to have affected him mentally as well since in that form he tricks Link (and gloats about it) while Link tries to enter the woods.
In God Hand, one of Shannon's more annoying moves in the first encounter with her is the ability to temporarily turn you into a defenseless chihuahua. She usually follows this move up by running toward you and punting you across the circus tent.
Chrono Trigger: In a subversion of sorts, Magus turns the knight Glenn into a frog. A frog the size of a small human, who can still wield a sword and actually seems to have better abilities in this form than as a human and later comes back for revenge. Greatjob!
This shows up in Chrono Cross; the party is volunteered for a magic show and turned into housecats. They're supposed to be turned back a few minutes after, but Sneff the magician throws his back out. You're left as cats for a while. This does end up having an effect in a few areas that barred other people from going through ... and let you grab an inventory item too.
In Wild ARMs 5, the Misery status turns your character into an adorable cat-version of themselves. Oh, and it disables all actions but Move. But it is also adorable.
The whole point of Disgaea 2 is to dispel a region-wide version of this at the source by defeating the Evil Overlord. Future games in the series reveal that it didn't actually work.
A gameplay example can happen as a result of one of the Dark Sun's effects, which will transform one of your humanoid or unique monster characters into a specific species of monster or a random one, depending on the map. It replaces the character's weapon skills with the skills of the species they transform into, but the special skills the main characters and cameo characters possess are retained, which can result in some hilarity.
In the Eggerland games (Adventures of Lolo trilogy inclusive), Lolo can use Magic Shots acquired from Heart Framers to transform his enemies into eggs.
Shiren the Wanderer features this trope a few times - in that "You are what you eat" is taken quite literally. Eating enemy Meat will turn you into that particular enemy. Though your HP and strength remain the same, you will be limited to that particular enemy's attacks and will be unable to use items. You'll also take on said enemy's qualities - some good (able to fire unlimited arrows, will regenerate on death, move at double speed) and some bad (will take heavy damage if hit in the back or side, move at half speed) You can also become immune to every enemy in the game by eating meat that makes you invisible - since no enemy can detect invisible creatures, no one will hit you (though you still may die of hunger.) The enemies are the true victims of this trope, as throwing meat at them will cause them to turn into that particular enemy - without retaining any of their previous stats. Keeping Mamel Meat around to toss at a Death Angel may save your life!
The witch from Mendel Palace uses her powers of transformation to morph you into one of the dolls from her houses. This turns against her in the Sumo level, as any attempt to try and flip you over will lead your character to counterattack with a sumo stomp and send her flying into the wall.
Arcanum's polymorph is described to turn the subject into any number of animals, but sheep were the most frequent. Few NPC's had and used this ability, and it was an effective neutralizer for any caster.
In Rogue you can sometimes find a Wand of Polymorph, which turns any monster you zap into another monster of random type. Depending on the RNG, you could indeed get a baleful effect (Dragon into Bat, for instance) ... or you could be toast (Dragon into Jabberwock, which is nearly as bad and now the monster has a free chance to attack).
Neverwinter Nights 2 features a 'mass fowl' spell, which can lots of enemies into chickens permanently, the verbal component sounds like chicken noises and cruel laughter. A similar 'mass frog' spell can be found in other variants of the D&D system.
Neverwinter Nights doesn't have it in vanilla, but the PRC as well as some custom haks in certain servers add this spell. It's called indeed Baleful Polymorph and transforms the caster into a chicken. Is one of the cases where the victim is heavily weakened, as he's reduced to a single hit point.
Lusternia's Wiccan class has Toadcurse, transforming players into an ineffectual (and easily stomped) toad for a period of time. Gods can also reduce players to maggots if sufficiently irked.
In The Elder Scrolls: Redguard the hero Cyrus is transformed into a scamp for a short part of the game.
One of the runewords in Diablo II has a chance of turning the user into an undead pigmy skeleton.
In MapleStory magicians get a skill called Doom, which temporarily turns monsters into snails. They retain the power level of normal snails, but in this game, small is deadly.
In Jak and Daxter: The Precursor Legacy Daxter is turned from human to ottsel when Jak accidentally knocks him into a vat of Dark Eco. Over time he grows to accept, and even like his new form, because when given the chance to return to normal, he settles for a pair of pants instead.
In Castlevania: Circle of the Moon, one of the card combinations turns you into a skeleton, a common Castlevaniaenemy. It had a weak attack and could be killed in one hit, but there was a small chance that it would throw a Big Bone, which could one-hit kill anything (even bosses).
Lands of Lore II: The Guardians of Destiny has Luther, protagonist and son of the original game's big bad. He's cursed to have uncontrollable transformations between his human form, a hulking beast, and a tiny swift creature. Over the course of the game, he finds a means to control these transformations.
However, Luther's transformations are anything but baleful. His beast form, while large and slow, grants super-strength, allowing him to push otherwise immovable objects out of the way, while his lizard form grants awesome magical abilities.
At one point in Ys II, Dalles transforms Adol into a goon (different from the kind achieved by the Transform magic), and he must find a cure.
In Achaea, one of the ultimate punishments the gods can use on mortals is "shrubbing" - turning you into a shrubbery. For all but the most foul offences, you will eventually get better.
Elves could use the "Polymorph Other" spells in Capcom's Dungeons & Dragons arcade games. It basically functioned as a Smart Bomb since the cute bunnies and frogs couldn't do anything to you and bounced off the screen.
Probably counts. In Bayonetta the final boss will throw spiral-galaxy shaped discs at the title character. If she is struck, she turns into a defenseless—and so slow that she might as well be motionless—child.
Star Ocean: Till the End of Time has a number of mook-class enemies called 'Masques' which possess the "Vegiform" and "Cutey Pie" special attacks. These attacks temporarily change the target into a vegetable or a pastry, respectively. The target of the attack is rendered immobile and helpless while in this form.
In each game of the Pokémon Mystery Dungeon series, you play as a human who's been transformed into a Pokemon. It's subverted in that their new form is far more suited to saving the world than that of a human's, though. It's revealed have been willful in Rescue Team, and unintentional in Explorers.
In Pokemon Mystery Dungeon Rescue Team, this was also the eventual punishment of the human now better known as Gengar, who abandoned a Pokemon companion for the sake of his own safety.
In the last dungeon in Golden Sun: The Lost Age, you encounter and battle two Flame Dragons. Surprise, they were your Fire Clan antagonists, and being transformed against their will like this has drained so much energy that they're freezing to death (averting the Never Say "Die" variant of this trope). And then you learn the hard way that the Wise One's "miracle" to stop you was turning your parents into a dragon and forcing you to fight it.
Happened also in the first game, when trying to cut down the guardian of the forest got the people of Kolima (and all non-Adepts who went to rescue them) cursed into trees.
In Portal 2, GLaDOSbecomes a non-magical variant when Wheatley converts her main core into a potato battery.
In NieR it turns out that all the Grimoire were originally humans who learned magic, and were forced into those forms to serve Project Gestalt.
In Solatorobo, Nero and Blanck turn into Caninu when The Order is given. Considering they considered themselves so much better than everyone else, the transformation upsets them greatly. Red himself is also transformed into his human Trance body, but he's less upset about the transformation and more upset about the mind control that comes with it.
Fantasy Quest: A dog turns out to be a man stricken with a curse, which makes you feel bad for having tried to play fetch with him before.
League of Legends' Lulu loves to leverage her powers of legerdemain against her litigants. Alliteration aside, she turns her opponents into small woodland creatures.
In Guild Wars 2, there is the elite Mesmer spell Moa Morph, which turns the target enemy into a Chocobo-like Moa for ten seconds. While not entirely defenseless (the pecks and kicks deal moderate amounts of damage), it greatly reduces the threat the target presents.
In Dota2, the this is the effect of the spell "Hex". The heroes Lion and Shadow Shaman have it, with the former's turning people into frogs and the latter's turning them into chickens. The item "Scythe of Vyse" turns people into pigs (Sheep in the original DoTA, leading to the nickname "Sheepstick").
In Dragon Quest VIII the main plot is about the heroes chasing after a rogue magician/jester who turned King Trode into an troll like creature, and his daughter Princess Media into a horse. Also... a man transformed into a short green creature chasing after a magic user with long silvery hair as well as being designed by Akira Toriyama. Sound familiar?
Done twice in the Wario Land series. In Wario Land 3, the entire population of the Music Box world was turned into the monsters Wario beats up throughout the game by Rudy the Clown. In Wario Land 4, Princess Shokora was transformed into the Black Cat by the Golden Diva after she lost in a magic duel. In both cases, the transformations happen before the events of the games, and are undone when Wario kicks the Big Bads' asses.
In Entomorph: Plague of the Darkfall the ruling class of an island kingdom are transforming commoners into giant insects to make them better workers and soldiers and more obedient. The hero fighting them ends up transforming himself too, because human body is too weak. The ultimate reveal is that the source of the transformative "juice" is the queen, transformed by a cursed scarab, planted by an agent of the setting's Biggest Bad. She will help the hero to kill herself and neutralize the scarab, but still will fight him ferociously.
In Robopon, Princess Darcy is imprisoned in a mirror, and her sprite 'becomes' the mirror until she's rescued—though oddly, there are no mirror-based Robopon.
Klonoa: Leorina's transformation into a giant robotic chicken-thing is imposed on her by the Bigger Bad.
In Sluggy Freelance, Torg gave Zoe a necklace one Christmas, having found it inside of an Egyptian pyramid. It turns out to be cursed, and transforms her into a camel. Her friends eventually learn the necklace's history and change her back, but the necklace ended up binding to her in the form of a tattoo, and a pair of magic words spoken by anyone can turn her into a camel ("shupid") or human ("kwi").
In-canon (and out), Grace occasionally gets hit with this trope...but she's a shapeshifter, so it doesn't do anything other than give her a new form to play with.
Princess Flibbage from Footloose has a notorious habit of transforming unimportant characters when she's annoyed.
In Goblins, a major battle had several polymorph effects occurring due Shield of Wonders. One guard was polymorphed into an ogre, and another became a soulspike destroyer. A few issues later, another guard is transformed over the course of several panels into dozens of snakes, which promptly go slithering off in different directions.
Trace hits the old Hight Templar with this; getting polymorphed in he Two Kinds setting is extremely painful. He made her look like a wolf Keidran (beast-man), and had the guards drag her off to a slave market. He also makes his ex-girlfriend's annoying little sister grow a set of cat's ears and thin fur, although it's unclear how "baleful" this was; she quite likes the look.
New World is largely based on this trope, as both Nicolo and Amanda love turning people into frogs, furries, or anything else comes to mind, usually throw genderbending into the mix as well.
Several characters in The KA Mics have been unwittingly changed into various things. It usually happens to Gertrude & Brunhilda.
City of Reality features the villain Hinto Ama, who wreaked havoc in the World of Magic with her transformation powers. Years later, the Manumitor is a man who seeks to undo the harm she caused by reversing as many of the transformations as possible, but is apparently capable of the same magic. This is because he is in fact Hinto Ama in disguise, seeking to atone for her past misdeeds.
In Crimson Flag Julian Urocyon found a staff that could transform Reyn into ordinary (non-anthropomorphic) foxes. He used it on the Red Queen and her bodyguard Bryce and planned to use it on the Red's entire military but was foiled by Lucian, though both of them were transformed in the process.
In Princess Chroma, the Mentor Mascot started out as a handsome Winged Humanoid with a variety of magical powers and immortality. Now he's a lop-eared bunny at the mercy—or lack thereof—of an ill-tempered middle school girl.
SCP-2950: It's just a chair. Nothing world-ending about it at all.Trust us.It is actually an anomaly that takes the form of whatever the majority of people think it is. A book describing it as an extremely dangerous monster used to mean that it was a monster, but after figuring out the true nature of the object, the Foundation wrote a fake document claiming it was an extremely comfortable metal chair and spread information of it among their members in order to turn the monster into said chair.
Dexter's Laboratory has a direct American Werewolf parody called "The Laughing" (a reference to the werewolf movie The Howling) where Dexter becomes a "were-clown" after being bitten by a pair of dentures belonging to a clown performing at Deedee's birthday.
Parodied in an episode of Futurama titled "The Honking", which had Bender turning into a psycho werecar in one scene. But after a while he kind of gets used to it and it begins to actually feel quite nice.
Gargoyles, "Metamorphosis". Elisa's younger brother gets transformed into a gargoyle-ish monster, and the only scientist who understood the process is killed. The episode ends with our cool veteran cop, Elisa, crying uncontrollably at the fate of her brother.
The subversion of this trope would be when the transformed hero is just as or even more effective in their new form, like that episode of Powerpuff Girls where Mojo turns them into dogs, but they manage to beat him anyway because...they're dogs with really sharp teeth and human intelligence.
And the trope is actually averted in the sequel to that episode, in which Mojo tries the exact same scheme. He tells the girls that he has studied the last time extensively, and has taken special precautions, including not turning the girls into dogs. Too bad he missed the fact that, untransformed, they're superpowered girls, and are free to beat him up in the usual fashion.
Happens to Wonder Woman in the Justice League Unlimited episode "This Little Piggy". She still has her bracers, at least. Still, Batman's reaction was...nonplussed◊. They then made a toy of Batman walking a pig. Why, nobody will ever know.
The Mad Scientist kid responsible for this had used his transforming machine for other purposes, like turning his entire PE class and coach into an ant colony (still doing the same climbing and running drills within their little ant farm, of course). When Arthur attempts to use the machine to turn the Tick back into his normal form, he struggles with the dizzying array of controls, turning the Tick into a blue dog, a blue sock, a blue houseplant, etc. before he finally notices the giant red button labeled "NORMAL" slightly to his right.
Partially subverted when The Tick rhapsodizes about how one can lay an egg and still feel like a man and protects his egg. Later turned in to squick when the egg is broken and he eats the chocolate.
Kim Possible was cursed with transforming into a monkey, but she got better (at the very last second).
The Monkey Talisman in Jackie Chan Adventures has the power to turn anything into any animal (and only animals; Jade found that part out the hard way when she tried to change a log into a death ray and got a manta ray instead).
There was also the Monkey King, an ancient mystical creature trapped as a puppet who turned people into puppets whenever someone pulled his leg. His first appearance features Jackie falling for it though Jade hits him with the Rat Talisman, letting him go around and eventually change himself back, while the second episode had a hapless construction worker fall victim to his curse.
During the season 1 finale fight against Shendu, Jackie stole the power of the Monkey Talisman and turned Shendu into a rabbit. Unfortunately Shendu still had enough remaining powers to be a Killer Rabbit, and promptly beat up Jackie and changed himself back into his demon dragon form.
The obligatory appearance by Circe in the ongoing cartoon of Disney's Hercules featured the personality polymorph, complete with Icarus, the resident weirdo, becoming a platypus.
One Episode of Teen Titans has the team transformed into various animals such as a bear, cat, monkey, rabbit and... a lamp? (Beast Boy had pointed out to the suddenly nonplussed villain how he transforms into animals already, so the villain had to pick something else. Even then, Beast Boy could still shapeshift, but only into various types of objects.)
A Time Travel episode of DuckTales included a meeting with Circe, who, of course, turned Scrooge into a pig. A Carl Barks comic also had Magica use Circe's wand to turn Scrooge's nephews into animals to blackmail him for his Number One Dime.
Metus being turned into a snake by the Ignika in BIONICLE: The Legend Reborn.
In the rebooted series of Yoohoo And Friends it is the central theme with polluting corporate executives being turned into cute, cuddly animals by Father Time and sent on missions to fix up the environmental damage they have caused.
A few times in My Little Pony: Friendship Is Magic. In a flashback, Twilight's Power Incontinence turns her parents into potted plants. In "Too Many Pinkie Pies", people keep interrupting her as she's practicing her Apples to Oranges spell, resulting in unfortunate orange/animal hybrids of a bird and a frog when her aim is thrown off.
This becomes a story point in the first season of Winx Club, where Mirta is turned into a pumpkin halfway through by Icy for both foiling her plan to break Bloom's mind and making an illusion so terrifying that it scares Darcy and Stormy and keeps them from killing the other Winx. The rest of the season contains several references to Flora trying to figure out how to change Mirta back; she manages to do so in the second-to-last episode, though she plays it up as being very difficult to do.
Later on Miss Faragonda is turned into a tree, but she gets better.
This is Krudsky's major form of attack once he gains magical powers in Scooby-Doo! and the Goblin King. He turns Gribbles into a rabbit, Velma into a werewolf, Fred into a vampire, Daphne into a witch and the Goblin King into a goose. Additionally, Shaggy and Scooby are turned into a snail and a mouse by the witches in the Dead Bogs.
The fate of many an individual unlucky enough to cross paths with the Magic Man of Adventure Time.
Besides a few times when humans have been turned into frogs, The Smurfs episode "The Noble Stag" has one instance where their friend King Gerard has been turned into a black stag by his cousin Malcolm the Mean, who desired to take over the throne.
German comedian Otto once told the story of Susi Sorglos, whose hairdryer claimed to be a transformed prince. This turned out to be a lie, it was actually a transformed razor.