The Grim Adventures of Billy and Mandy (2001)

S6E1 Billy Ocean

During a trip to the beach, Billy, Mandy, and Grim encounter Blubbery Joe, a whale that swallows Billy whole. Inside the whale's belly, Billy meets Mister Geppetto and Pinocchio, who are both trapped there. Longing for a genuine son, Geppetto persuades Billy to take on that role, sparking jealousy in Pinocchio, who plots to consume Billy in hopes of becoming a real boy and winning Geppetto's affection. Meanwhile, Mandy and Grim team up with Captain Deadwood, a wooden pirate obsessed with hunting Blubbery Joe. Eventually, Billy, Geppetto, and Pinocchio are expelled from the whale, leading to a surprising resolution where Blubbery Joe agrees to be Geppetto's son.