The Grim Adventures of Billy and Mandy (2001)

S6E3 Keeper of the Reaper

After Billy's father receives a job promotion, he announces the family's upcoming relocation, sparking a rivalry between Billy and Mandy over who will keep Grim. To resolve their conflict, Grim proposes they take their case to court. Soon enough, Billy, Mandy, and Grim are in the Underworld courtroom, where they face Judge Roy Spleen, and Fred Fredburger, a hilariously clueless juror. As tensions rise, the trio navigates the absurdities of the trial in a bid to determine Grim's fate.