Doomsday of UAC



Doomsday of UAC (commonly known by its filename UAC_DEAD) was released in 1994 by Leo Martin Lim as one of the first fan-made PWADs. It was considered one of the top 100 Wads of All Time by Doomworld as part of their 10 Years of Doom celebration.

UAC_DEAD features an attempt at creating realistic looking vehicles and environments. It has a replacement sky texture (taken from nightfal.wad) and the first use of the self-referencing sectors trick, used to simulate both invisible stairs in the style of the film Indiana Jones and the Last Crusade and an invisible chamber enclosing a Cyberdemon. Careful flat and texture choices are used in places to simulate coloured lighting.

Bugs
The map occupied the E1M8 slot in order to use the special tag 666 twice, exploiting a peculiarity of Doom's handling when more than one boss monster is present in the map. This peculiarity was changed in Ultimate Doom v1.9, and as the Doom source release inherited this change, the map is unplayable with many modern source ports. Both Chocolate Doom and PrBoom have settings which allows to play it as intended, and current SVN versions of ZDoom identify the level through its checksum and automatically apply the correct compatibility flag.