Dromed 101: If you do anything custom involving textures or making new archetypes in the hierarchy, you have to save your gamesys.
- Save gamesys as something.gam
- Enter the command set_gamesys something.gam
- Save your mission
Alternatively (and more easily), just save as a .cow file instead, which includes both the mission and the gamesys in one file, while you work on your mission. Then do the steps above only when packaging up for testing or giving to others (.cow files are only for Dromed, Thief2 requires the separate .mis and .gam files).