Like the other members, he wears an all black outfit with yellow stripes on the arms. His head is in the shape of a thumb with hair that looks like a nail.
Not much is known about his abillities except he appears to have brutal stength and every part of his body appears to be strong.
He first appears in Last Laugh where he and the other Circus Freaks are working for Zombozo. He is presented as a preformer in Zombozo's show where he introduces himself to beable to bend a pipe. Later he and the other Circus Freak members are robbing a store when Wildmutt shows up to stop them. Thumbskull is defeated but gets help by Zombozo and escapes. In the end of the episode he helps the Circus Freak Trio guard the circus. When they are attacked by Upgrade who merged with a baseball machine, he is no match and quickly is defeated.