Doom: The Lost Episode is a 9-level episode PWAD which aimed at creating a thematically consistent fifth episode for The Ultimate Doom with maps taken from the alpha, Jaguar Doom and PSX Doom and then "remastered". It was developed to be compatible with both ZDoom (and derivatives) and the Eternity Engine. To reinforce the "pseudo-official" aspect of the mod, an intermission map is provided (in ZDoom). The endgame graphics uses a vertical scroll like Heretic episode 3.