Effect - Code

E1M9, Military Base - Find secret exit in E1M3, Toxin Refinery. The secret exit is located across the pit of slime near the entrance of the level.
E2M9, Fortress of Mystery - Find the secret exit in E2M5, Command Center.
E3M9, Warrens - Find the secret exit in E3M6, Mt. Erebus.
E4M9, Fear - Find the secret exit in E4M2, Perfect Hatred.The secret exit is north of the Cyberdemon.