MarsDoom is a partial conversion for Doom II. The wad was created by Berthold Beckschaefer and Thomas Lokum, and was later legalized by Sparky of KISS Software. Currently the only version available is a preview version, which contains about 9 levels that were probably going to be from the completed project.
After the events of Doom II, the UAC announced that all teleporter technology was to be scrapped and their research bases were to be abandoned. However, the teleportation research as well as studies on the demonic invaders was continued on the UAC base stationed on Mars. After roughly seven months of quietly-conducted research, all contact on the UAC base on Mars was lost and, a day later, Eileen O'Hara, daughter of the scientific co-ordinator of the Mars base, sent a distress signal to the UAC's headquarters while it was still investigating the loss of contact. Following the distress signal, the Doomguy set off to Mars to take care of the Hellspawn once again, rescue any survivors, and arrive back in one piece.
The game was drastically changed, and featured turrets that would fire at the player unless deactivated, new enemies, and many impressive map tricks not often seen in a WAD created before 2001. A couple of levels required the player to escort someone else to the exit before the player himself could exit the level. There is some nudity, although it is only apparent for a certain person that the player must escort to the end of a couple of levels. Due to the many changes via DeHackEd, the Zombieman, Shotgun Guy, and Heavy Weapons Dude are absent from this WAD.