Diaz: Last Hours of Purity is a gameplay mod by Corwin Brence (WildWeasel) and Marty Kirra, released in 2008. It received an honorable mention at that year's Cacowards under the category "This is my Boomstick".
As the latter name suggests, most content is in the form of new weapons, such as military-style pistols and assault rifles. GZDoom build r183 or later is required.
An updated release appeared later in the year as part of "WildWeasel's Hits Collection". It removed several weapons, added random monster spawning and a second playable character, and rebalanced the difficulty (most observers seemed to think it was harder). That compilation also retroactively established the Weaselverse series, of which Diaz is part. A third version has been in progress for some time; at least one beta package was made available in 2011.