Frog Song

Frog Song, also known as Pond's Chorus, Song of the Toad, and Toadsong, it's a Blue Magic spell and a Bardsong that inflicts the target with the Toad Status.

Final Fantasy IV
In the Nintendo DS version, Edward can learn Toadsong at level 20. It can also be used through the Sing Decant Ability as long as the character has it equipped and is at the necessary level. In all non-DS versions, this ability can only be used by using the Bardsong command while Edward is a Toad.

Final Fantasy IV: The After Years
Edward is able to use Toadsong with the Sing command again. It has the same effects as in the original game.

Final Fantasy V
Pond's Chorus, originally known as Frog Song and Toad Song, is a Blue Magic spell that turns the opponent into a Toad at the cost of 5 MP. It can be learned from Azulmagia, Elf Toad, Archeotoad, Kornago, Farfarello, Gilgamesh, Lemure. It can also be learned from Vilia if the player controls the enemy with a Beastmaster. In order to learn it at its absolute earliest, from the Elf Toad, the enemy must be alone in order for it to even use the spell.

The player may utilize this ability by catching and releasing an Elf Toad, Archeotoad, or Kornago.

Final Fantasy VII
Frog Song is an Enemy Skill learned from the enemies Touch Me, Toxic Frog, and Christopher. In addition to turning/curing one target into/of a Frog, it also puts it to Sleep for a cost of 5 MP.

Due to an error in either the coding or the writing, the spell's description claims it affects all enemies, while it only affects one.

Final Fantasy XI
Frog Song is an enemy ability that is not learnable by Blue Mages. It can be used only by Poroggo and inflicts a Costume status effect, turning the player into a frog, as well as Charming them. Some Notorious Monster versions have an upgraded version called Frog Chorus that applies to a group of players.

Final Fantasy Tactics Advance
Animists can learn Frogsong, which inflicts Frog. The ability is learned for 200 AP through the Aona Flute, and costs 18 MP to use.

Lamias can use Poison Frog which inflicts Poison as well as Frog.

Final Fantasy Tactics A2: Grimoire of the Rift
Animists and Lamias retain their Toad-status moves, though the former's move is known as Toad Song. It can be learned from the Blueleaf Flute for 400 AP and costs 22 MP to use.