S05E09 - Napoleon Bonafrog: Colossus of the Swamps
Synopsis
(synopsis credited to Ninjaturtles.com)
While Krang hires some local hoods to drill for anti-freeze (in an effort to free the Technodrome from the frozen Arctic), he sends Shredder, Rocksteady and Bebop down to the Louisiana Swamps in search of the Mutagen Pool. Shredder's mission is to extract said mutagen with the Mutagen Shooter to use against the Turtles.
Napoleon Bonafrog contacts the Turtles when he sees Shredder and crew patrolling the swamps and then inadvertently is blasted by the Mutagen Shooter when Rocksteady trips over a root, causing him to mutate into a mean giant frog. Shredder uses this to his advantage and returns to the City with his new ""slave"" in tow.
In the sewers, Napoleon reluctantly leads Shredder, Rocksteady and Bebop in the Turtles' lair. But before he is close enough, the mutagen wears off and he reverts back to his normal size and warns the Turtles off. Shredder zaps him again, causing him to mutate yet again. Shredder orders Napolean to destroy the Turtles