How many movies have Joan Gerber and William Hanna collaborated on?

They have worked on 4 movies together! Their first movie together was The Banana Splits in Hocus Pocus Park (1972) while their highest rated movie together was Scooby Goes Hollywood (1979). They have not worked together since Scooby-Doo! and the Reluctant Werewolf (1988). They are most known for their animation films together.