Donald Duck is turned into this form when he visits Atlantica. While in this form, he is half-duck on the upper part and half-fish from the waist down.
Kingdom Hearts
In the first game, Donald is able to use magic he's learned from other worlds and fight with his wand.
Kingdom Hearts II
In the second game, Donald's ability to use magic is removed as the design of Atlantica is converted to a world whose story progresses via songs.