Clark was a key player in the development of the XR-SIM Mission Rehearsal project, where he played a vital role in creating the user interface system and various features such as teleportation, shrinking player to tabletop, and enemy behaviors and objectives. He also contributed to the multiplayer aspect of the project, working closely with other engineers, artists, audio engineers, and producers to ensure the project's success. Although not shown in the video recording, Clark demonstrated the effectiveness of the multiplayer feature by joining a multiplayer session during the development process. His collaboration and expertise helped bring the project to life and deliver an immersive simulation experience.