Doom: Episode 5 (cancelled expansion to first-person shooter game; 1995)
In its final "Ultimate" version, Doom had a total of four episodes with eight levels and a bonus level each (some home ports, like the Jaguar and Xbox versions, had additional stages, but often lacked the fourth episode). However, John Romero recently released many assets of Doom development to the public. Among the more fascinating artifacts of this development dump was a level labeled "E5M1", implying a fifth episode to the game was in production but ultimately scrapped.
The opening shot (seen in the infobox) showed a hall of barrels near two Barons of Hell, implying this may have been a special non-canon challenge episode. Little else is known about the possible episode and what its content would have been.