When new settings stop a game from starting

Superposer remembers the settings of the last session that worked (the game reached its first picture and ran for 30 seconds). If you then change a setting that needs a restart (graphics, window mode, resolution, Wine settings, or words in the game's Steam launch options) and the game doesn't start, crashes or quits at once, Superposer switches back to the settings that worked, once, and tells you on the game's page and in a notification. Try again anyway puts the new settings back, and they are not switched back a second time. Words typed into Steam's launch options can't be edited while Steam runs, so Superposer sets them aside at launch instead and says so; change them in Steam when you like.

Safe mode. Hold Option while the game starts (from Steam or from Superposer), or add SUPERPOSER_SAFE_MODE=1 to the game's Steam launch options (for a controller-only setup; a controller combination can't be read that early). The game starts with the settings that worked, or with the recommended settings when none are remembered.
Reset this game's settings. Always on the game's Settings tab (and on the notice): deletes your saved settings for the game, and what Superposer remembered as working.
Test runs started by Superposer itself (Test, superposer smoke) never take part.