Game crashes with code:
The game crashed whilst initializing game
Error: net.minecraftforge.fml.ModLoadingException: Supplementaries (supplementaries) encountered an error during the common_setup event phase
Exit Code: -1

Got in once when deleting the pack and reinstalling. Then same again after I closed and relaunched

Im having exactly the same problem

Game crashes with code: The game crashed whilst initializing game Error: net.minecraftforge.fml.ModLoadingException: Supplementaries (supplementaries) encountered an error during the common_setup event phase Exit Code: -1

Got in once when deleting the pack and reinstalling. Then same again after I closed and relaunched

I had the same error code but once I removed Optifine from the mods folder it launched the game perfectly. Haven't had the error code pop up once in the 5 or so times since removing Optifine

yeah optifine is broken on the new forge so I would stay on that last update until forge is stable and optifine updates.