Events/FMLCommonSetupEvent/1.18

This event is a parallel dispatch event - you must use event.enqueueWork to interact with the game state in any way.

CommonSetup is fired after all the Events/RegistryEvents, but before the Events/FMLClientSetupEvent and Events/FMLDedicatedServerSetupEvent. This makes it useful for non-specific mod setup.

Register it any way you would normally register an event.