The Munsters - Season 1 Episode 20 Bats of a Feather

Eddie needs an impressive pet to take to the school pet fair, but Spot, the fire-breathing monster, is too shy to come out of hiding. Eddie decides to take Igor the bat, but Igor is insulted by one of Herman’s wisecracks and flies away. Without Eddie’s knowing, Grandpa changes himself into a bat to impersonate Igor. This causes trouble when Eddie gives Grandpa to another student whose father wants to send him to outer space on a scientific mission.