The Champion of Justice (1944)

A Terrytoons cartoon released 17 March 1944. An elderly couple (human, not animal) dies, leaving their substantial estate to their mice, who had befriended them. A distant nephew, Willy the Spender, is outraged, and he takes the mice to court in an effort to destroy them! The judge decides in favor of the mice. This really whizzes off Willy the Spender, and he goes after the mice! Can Mighty Mouse save them in time?

Animation, Comedy