S12E1 : Treehouse of Horror XI

This year's Halloween story sees The Simpsons as "The Munsters" (with everyone except Lisa getting killed), Homer as a wandering spirit on the hunt for a good deed in "G-G-Ghost D-D-Dad," Bart and Lisa as peasants in a fairy tale forest in "Scary Tales Can Come True," and Lisa inadvertently dooming mankind by rescuing a dolphin in "Night of the Dolphin."