Doomsday of UAC

Doomsday of UAC (commonly known by its filename UAC_DEAD) is a single-level PWAD designed by Leo Martin Lim. As part of their 10 Years of Doom feature, Doomworld named it one of the ten best WADs of 1994.

One of the first ever fan-made Doom mods, UAC_DEAD features an attempt at creating realistic-looking vehicles and environments. It contains a replacement sky graphic, and uses careful flat and texture choices in places to simulate colored lighting. It also includes the first known instance of the self-referencing sectors trick, used to create invisible stairs.