The Grim Adventures of Billy & Mandy

Night of the Living Grim (2x4)

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Grim is lying sick in bed with "Encroaching Doom Syndrome". The Underworld doctors are not able to help Grim, and he becomes a human being. Back in Endsville, Grim is apparently attractive to women, but he ends up being punched by jealous boyfriends, especially Billy's dad Harold. In the end, Grim covers himself in the mucus that he produced when he was sick, and becomes a skeleton again. Billy tries it too.