Grim or Gregory was the first Halloween episode of the Cartoon Network original series The Grim Adventures of Billy & Mandy.
It's Halloween, and Billy, Grim and Mandy go trick-or-treating. While Billy and Mandy are at a house, Grim mistakes a boy's mother for Atrocia, the host of the all-night Halloween Marathon on TV. Gregory is mistaken to be Grim by Billy, and Grim is mistaken as Gregory by Gregory's mother. In the end, everything is back to normal.