The River of Forgetfulness is a river seen in the episode "Death in Bloom." It is located in the Land of the Dead. If someone drinks the water or jumps in it, they'll lose their memory. Jake did drink the water from the river, therefore he lost his memory. It can only be revived by the Kiss of Death by Death, who must kiss you on the lips. Peppermint Butler told them not to drink the water from the river upon entering the Land of the Dead, but the two left too quickly to hear him. There is also a skull that tells people to drink the water, so they'll lose their memory.
- It is most likely based on the river Lethe in Greek Mythology, which was one of the rivers of the Greek God of the underworld, Hades.