MAP21: Slayer is the twenty-first map of The Plutonia Experiment. The music is the same as for Doom II's intermission text screens, and indeed there is a text screen just before this level starts, and since players don't usually let the text screens more than a minute, playing this level is a certain way to hear the whole nearly five-minute music track. The shape of the level draws many key features from MAP11: Circle of Death, but the player's progression through the level is completely different.