Doom: The Lost Episode
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.
Although reception was mostly positive, the mod has been criticized for the weirdness of its "surreal space" theme and the use of Doom II elements (including the super shotgun and several of the monsters) in a Doom episode. It later inspired another mod, known as The Console Doom Integration WADs, which was designed to be more authentic in terms of the console maps. It acts as an additional "episode" to Doom II instead though.
The "lost episode" is entitled "Evil Unleashed" as an allusion to the Doom Bible.