The 1966 T.V. Batmobile was created from a decade-old "concept show car" designed and built in 1955 by Ford's Lincoln Division. It was called the Lincoln Futura, and was originally a pearlescent pale green. After several years on the car show rounds (and an appearance in one movie, repainted red), it was sold for $1 to George Barris who stored it outdoors for 6 years. When FOX called looking for Barris to build a car for the show, they gave him 3 weeks, so he grabbed this already-weird looking car he had out back, sketched a few changes and passed the physical work to Bill Cushenberry. It was finished on time and the rest is history.
In his appearances as The Joker, Cesar Romero's moustache is visible under his makeup. Romero refused to shave it off, so his makeup had to be applied over it.
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.
The guest cameo in this episode is by Ted "Lurch" Cassidy, who appears at the window as Batman and Robin climb up the side of the building. Batman advises him to go back to playing his harpsichord - which has been regaling us with the theme from The Addams Family since the scene began.
Originally, Batgirl's mask came to points below the eyeholes. It was reshaped when the producers realized that the points left noticeable dents in Yvonne Craig's cheeks that took awhile to go away.
Celebrity cameos became a running gag on Batman, with the star usually sticking his or her head out the window as Batman and Robin climbed the building via Bat Rope. Among the many famous faces were Jerry Lewis, Phyllis Diller, the Green Hornet & Kato, Milton Berle, Sammy Davis Jr., Werner "Col. Klink" Klemperer, Ted "Lurch" Cassidy, Steve Allen, Don Ho, Jerry "The Beaver" Mathers, Art Linkletter, Alan "The Skipper" Hale, Edward G. Robinson and George Raft.