[[Image:Udmxmap20.png|thumb|right|200px|UDMX MAP20, by [[liam]]]]
After undergoing several years of sporadic and aimless work followed by an entire year devoted to its renewal and completion, the fourth installment of the series was released on December 31st, 2008. UDMX is the first entry in the series to fully replace [[Doom II]]'s original 32 levels, several of which are replaced by remakes ("flashbacks" as called throughout the WAD) of maps found in UDMX's predecessors. Unlike UDM3, the WAD uses a rich variety of custom textures and boasts a new palette that saturates reds and greens and deepens blues. While under development, the project underwent a series of name changes: initially called what it is now, it was eventually renamed "UDML" (Unidoom DM Legends), then briefly "UDMC" (Unidoom DM Classic), and lastly UDM4; however, it was soon decided that it would return to its original title. UDMX celebrates [[Unidoom]]'s 10th anniversary, bearing the "X" in its name to represent the ten years that had passed since the original 1998 founding of Unidoom at the time of the WAD's release. At a whopping 20.7 megabytes, UDMX is the largest UDM installment by file size. UDMX has received much critical acclaim throughout the community, deemed by reviewers as the best installment of the UDM series and one of the greatest deathmatch megawads to have ever been made. A [http://www.youtube.com/watch?v=Z9ZU-SxMo_Y trailer] for it was released on March 23, 2008. A [http://www.youtube.com/watch?v=TgdIixFx1i0 follow-up trailer] showcasing newer maps was released on August 28, 2008.