Doomsday Junior High is the junior high school that Grim attended, along with other underworld characters. It was shown in the Billy & Mandy: Wrath of the Spider Queen special episode. A 130,000 years ago, the school's principal was Judge Roy Spleen.
In the storyline of Billy & Mandy: Wrath of the Spider Queen, it is the main setting of the flashback that Grim shows Velma, so that she is able to understand why he was made the reaper and not her. This