Double Impact, sometimes know as the E1 Replacements is a mod for DooM, meant to be a replacement for Knee-Deep in the Dead, the first episode from DooM, developed by Ralph "Ralphis" Vickers and Matt "Rottking" Cibulas that was released on November 30th, 2011. It features larger combat arenas, more emphasis on exploration, more "space-like" views, and more dramatic lighting effects. Other than a few new musical tracks, it is completely vanilla. It received a Cacoward in 2011.
- The music track for E1M2: Central Computing is a mash-up of the tracks "Dark Halls," "Suspense," and "Demons from Adrian's Pen"
- The music track for E1M8: Launch Bay is a remix of the track "Phobos Anomaly"