Simon worked on several unreleased levels before forming Team Onslaught in 1997 with Tom "Mystican" Robinson, Luke "Spike" Cama, and Vincent "Vicious Killer" Fong. While part of Team Onslaught, he developed a Doom launcher called Onslaunch in 1998 and contributed to the deathmatch WADs Decamatch and Decamatch II: Annihilation. After Team Onslaught dissolved, he contributed to Execution DM along with several former Onslaught members. In 2001, Simon took the lead role in the development of the Freedoom project, a project aiming to create a complete free IWAD file.