In O Brother Where Art Thou, a retelling of The Odyssey, Delmar is at one point convinced the three "sirens" (seductive washerwomen) have done this to Pete. In fact, they've turned him in to the authorities.
In The Black Cauldron, Fflewddur Fflam gets turned into a frog by one of the witch sisters who wants to eat him, but he gets changed back by the one who has a crush on him.
Whenever the various sorcerers of the Belgariad are in trouble, the first thing nearby muggles suggest is that they transform the enemy into something harmless, usually with a mystical hand gesture. Polgara once turned a Cherek king into a man-sized frog so that he would take her seriously.
Witches and Wizards alike in the Discworld can do this, but tend not to because it takes a lot of effort. Granny Weatherwax, particularly, prefers to simply make the victim think they've been transformed.
In Witches Abroad, the witch Lily Weatherwax inverted this trope, turning a frog into a prince so he could rule as a figurehead under her control.
In Going Postal, one of the bankers threatens to sue Unseen University in the heat of the moment. Archchancellor Ridcully's reply?
Ridcully: Oh, please sue the University! We've got ponds full of people who've tried to sue the University!
In The Wee Free Men, the toad who joins forces with Tiffany and the pictsies used to be a human lawyer, until he helped a client sue her own fairy godmother. Bad move.
Morwen, the resident good witch in the Enchanted Forest Chronicles, is offended at the suggestion, although she considers doing it to Arona Vamist because he irritates her so much. Her cats encourage it as they want something to play with.
In The Lord Of The Rings, when Sam is caught eavesdropping on Frodo and Gandalf's conversation about the One Ring, he begs the wizard not to turn him into "anything unnatural", and Frodo insists it'll be a warty toad if Sam doesn't keep his mouth shut. Since it's a fairly low-magic setting, by modern fantasy considerations, it's unlikely that Gandalf could actually do it if he wanted to.
In Tom Holt's Falling Sideways, intelligent alien frogs who came to Earth long ago have the power to make themselves seem human, and to make humans appear and act like frogs. The prince isn't really a frog, but the princess is!
Harry Dresden has jokingly threatened to turn people into toads. Though it's an empty threat as unwilling transformations are against the White Council's laws.
In Pamela Dean's Secret Country books, a character uses "Shan can turn you into a toad!" as an expression of annoyance, referring to a legendary wizard named Shan.
In A Bad Spell For The Worst Witch, Mildred tells Sybil and Clarice that she thinks Miss Hardbroom did this to a girl who became the frog she's seen in the school pond. Later in the book, Ethel turns Mildred into a frog. Whilst in her frog form, Mildred meets the frog in the pond who it turns out is a wizard who got into a fight with another wizard and ended up stuck as a frog when the latter cast a spell on him.
In Yendi, it's mentioned that Sethra Lavode, one of the world's most powerful sorcerers, sometimes turns intruders into jhegaala. The jhegaala is an animal that metamorphoses repeatedly in its life, but resembles a toad at one of its life-stages. Also, the Sorceress in Green threatens to turn Vlad into a newt in the same novel; his retort is a Shout Out to the Crowner, above.
Zigzagged in Dungeon of Dread, a pick-a-path book based on the D&D game. The Evil Sorcererturns innocent villagers into animals, including one who became a toad ... not a helpless one, as this trope usually features, but a giant toad large and fierce enough to guard his lair.
Forgotten Realms got some of this: From the introduction of Volo's Guide to All Things Magical, 2 ed. --
Elminster: To readers who trust in the sword or the dagger and hope to find in these pages a guide to how to lay mages low, I tender the following piece of very good advice: "Wizards? Avoid 'em. Life's better when ye're not a frog." That anonymous trail saying of the Sword Coast lands has been around a long, long time, but it is best never forgotten--if ye take my point.
"Why, Dhaerivus, I recall my first magefair!" He nodded in reflection and added dryly, "Ye made a most fetching toad."
Dungeons And DragonsForgotten Realms setting, supplement Pages from the Mages. During the course of a feud between the wizards Phelpar of Rassatan and Selvar of Taruin, Phelpar turned Selvar into a frog. Selvar had to hop many miles to reach a cave where he had hidden a cache of magic that could return him to normal.
In the 5th and 6th editions of Champions, the superheroine Witchcraft is built as a standard superhero-mage ... but has a spell to turn people into frogs. One of the "cure" conditions is even being kissed.
Frog in Chrono Trigger got his moniker and his shape from Magus, the Disc One Final Boss, who saw the young Glenn as a harmless foe and wanted to humiliate him. If you let Frog kill Magus in the Duel Boss near the end of the game, he will have reverted to his original form by the end credits.
In Final Fantasy III you are capable of turning your enemies into Frogs with the Frog spell and at one point have to turn yourselves into Frogs to progress.
In Final Fantasy IV (II in the US release), not only are there in-battle frog (and pig) transformation spells, but at one point the townspeople turn you into frogs and pigs for revenge for your earlier actions as the Dark Knight.
Additionally, there is an enemy called the Bog Witch, who enters battle with several Bog Toads and orders them to cast Toad on you every round. When they're all killed, she turns herself into a Toad.
The witch Styx turns the world-famous bard Eduardo into a frog after promising him a way to be together with the mermaid he loves. The spell is only broken by the mermaid's kiss, with the twist being that the mermaid is actually his mother and the kiss is on the forehead.
World Of Warcraft plays this straight as an arrow with the Shamans' Hex ability. Mages get something similar, but it turns their targets into sheep...or monkeys, penguins...you get the idea.
In Crash Bandicoot 3 Warped, getting hit by a wizard's "energy blast" in Medieval stages turns him into a frog, costing you a life.
In Scribblenauts, the magic wand (which is the default weapon of witches and wizards) shoots bolts that change living things into frogs.
In Escape From Moonbase Alpha, Deadly Doris (an animated television set, possibly inspired by Evil Edna in Willow The Wisp), has a chance of turning the player into a frog when she attacks.
An odd example (subverted inversion?) is in Video Game/Glover. You can cast the frog spell onto witches, but they will reverse the spell right back at you.
In Jazz Jackrabbit 2, there's a witch that turns you into a frog, and being kissed by Eva Earlong turns you back into a hare. There is only one only place where this happens, and it is in the demo levels.
In Cave Story, Misery turns Balrog into a giant frog for a boss battle.
In Kings Quest V, the witch in the forest has turned numerous people into frogs, and can turn Graham into a frog as well.
Mages have a reputation for doing this in Dragon Age. In fact, Alistair can say that he prefers to know his odds of becoming a toad at any given moment.
An Inversion in the Simpsons Treehouse of Horror parody of Harry Potter: students are expected to turn frogs (presumably of original frog descent) into princes.
In a Fractured Fairy Tale from Rocky And Bullwinkle a princess finds a prince which has been turned into a frog. He wants her to kiss him to turn him back into a prince but she refuses. "A talking frog! I'll make a fortune!"
In Shrek the Third, King Harold gets turned back into a frog after being turned into a human by Fairy Godmother.
Five hats means that five tropers think it is ready to publish.
You are saying that you think this draft is ready to be published. That means the description is not ambiguous,
it doesn't duplicate an existing trope, there are at least three examples, and the title makes sense.
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You are saying this draft has a ready-to-publish hat it does not deserve and you are taking it back.