I don't remember which Doom this's from, but it starts in a small, dark room, with lots of ammo, then you teleport into a bigass green room with a huge toxic pit. There, the strongest monster sin the game (CyberDemons, Mancubi, Arch-Villes) spawn for a long time. I've beaten it once, and only once, on "Hurt me Plenty". Maybe one of you recognize this level.