ASDOOM][: The Final Countdown (ASD2.WAD)

Andy Sheppard released his ASDOOM back in '94, an episode 1 replacement for the original Doom. The following year, he published ASDOOM][: The Final Countdown, an eight-map episode for Doom II. The basic idea is the same, a series of levels with little consideration for 100% completion for pistol start. It's not a true sequel, though. When Sheppard put out ASDOOM, he must not have known Doom II's story, because the plot involved the marine returning from Hell only to be immediately thrust into a mission to a UAC base on Jupiter's moon, Io. ASD2 drops that concept entirely, as though it never happened. It's actually a followup to Doom II, starting immediately after your battle with the Icon of Sin. You return to Earth to find that the evacuation fleet is locked in some kind of stasis and needs your help in slaying the demonic remnants holding them back. One Colonel Diaz is your liaison, and she has several tidbits of wisdom to offer between MAP03 / 04 and MAP06 / 07, which you can read in Sheppard's voluminous .TXT.

ASDOOM (ASDOOM.WAD)

Andy Sheppard crafted two episodes, one for Doom and the other for Doom II, back in 1994 and '95, respectively. This is ASDOOM, an E1 replacement, consisting of nine levels. Sheppard places the level's story immediately following the original Doom, before the plot of Doom II was known. You emerge from the teleporter at the end of Inferno and arrive on Earth, with your superiors debriefing you for all the information you have on your encounters, because while the demons never made it to Earth, the UAC did lose contact with their Io base, which was executing the same kind of gateway experiments. As was the case with Ripley, you're sent as an adviser as you're the only human to have encountered the forces of Hell and survive. Of course, when you arrive, the forces of Hell wreck your dropship and you're forced to fend for yourself, fighting your way from the deepest level of the base to the top.