Beetlejuice (1989)

S4E46 Forget Me Nuts

After Beetlejuice gets knocked out and loses his memory due to an accident with a satellite, Lydia decides to take him to Dr. Zigmund Void for help. The doctor ends up splitting Beetlejuice's personality and shrinks himself and a clone of Beetlejuice down to travel inside his body in a tiny submersible. Together, they must uncover the reason behind Beetlejuice's memory loss before they revert to their normal size, racing against the clock to restore his mind.