Teenage Mutant Ninja Turtles (1987): Season 1, Episode 5

1 - 5: Shredder & Splintered

Shredder creates a retro-mutagen gun that can undo any mutation and dares the Turtles to come get it. As Donatello tries to create a fuel source for the vehicle that The Nutrinos left behind, Splinter and the Turtles eventually make their way to the Technodrome just in time to discover Krang in his new body.