Basil Karlo was an actor who became insane when he learned that a remake of a movie he starred in, The Terror was in the works, even though he was a member of the advising staff. Karlo went on a murder spree dressed as the movie's villain, Clayface, and kills most of the remake's cast and crew, saving the actor in his old role for last, but Batman and Robin (Dick Grayson) intervened. After several other schemes, Karlo was visited by Sondra Fuller, the fourth Clayface. Karlo suggested that he, Fuller, and the other living Clayfaces form the "Mud Pack" and attempt to kill Batman. The "Mud Pack" failed, but Karlo was able to transfer the powers of Fuller and Preston Payne (the third Clayface) unto himself, which transforms himself into an actual Clayface (rather than dressing up as one) with all the powers of the others.
- Ability: Copy cat (Can mimic almost any villain, except for Lex Luthor and Ra's Al Ghul, and receive their ability for the day, as long as it is not a bonus health point. You may still mimic a character with a bonus health point to mimic their bonus against another character, if they receive one.)
- Weakness: Copy-cat (cont.) (You will also receive any weakness of a character you mimic for the whole day.)