Teenage Mutant Ninja Turtles (1987): Season 4, Episode 2

4 - 2: Turtles of the Jungle

A professor's new ray-gun causes plants to go wild and his pet ape Jocko to become a giant rampaging monkey. By using the same ray-gun, Donatello is increased to Jocko's size so he can fight the giant ape and save April from him