Paddle ball is a one-person game played with an attached ball and paddle. Using a flat paddle with a small rubber ball attached at the center via an elastic string, the player tries to hit the ball with the paddle in succession as many times as possible. The paddle is usually made from either wood or plastic, although other materials can be used.
Marvin was using a paddle ball when he was in the Hall of Justice's recreation room. He bragged to Wendy that as a table tennis player, he could likely beat "the champion of China." Wendy then asks who his opponent is, suggesting it may be The Invisible Man.