The Entrancing Dr. Cassandra - S3-E25
Trivia: Cassandra springs all the arch criminals from prison. We see Joker, Riddler, Penguin, Egghead, Catwoman and King Tut and hear them laughing (dubs of the original actors' voices). But a close look reveals them all to be doubles. Apparently the budget didn't cover paying Cesar Romero & co. to appear in such a short scene. (00:15:30)