Events/FMLCommonSetupEvent
From Forge Community Wiki
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.