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)
Answer: It's wasn't unusual for multiple actors to play one character on this show. The villains on the TV Batman were played by guest stars, not regular cast members. George Sanders, Otto Preminger, and Eli Wallach played the part at various times. They may simply have only wanted to play the part once or twice, or they were later tied up with other projects, making it necessary to cast someone else. Other characters, like Catwoman, were also played by more than one actress.
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