I have an @SubscribeEvent method that is called whenever the AttackEntityEvent is called. Whenever it is called, the game crashes. Here is the code:

 

@SubscribeEvent
public static void onAttack(AttackEntityEvent event) {
    /*
    if the entity who attacked was a player and was holding a t3 core then it is set to t4
     */

    PlayerEntity player = event.getPlayer();
    int count = player.getHeldItemMainhand().getCount();
    ServerWorld world = (ServerWorld) event.getEntity().world;

    if (event.getPlayer().getHeldItemMainhand().getMaxDamage() >= 15) {
        ItemStack stack = ItemRegistryHandler.T4_CORE.get().getDefaultInstance();
        stack.setCount(1);
        player.setItemStackToSlot(EquipmentSlotType.MAINHAND, stack);
        ItemEntity item = new ItemEntity(EntityType.ITEM, world);
        stack.setCount(count - 1);
        item.setItem(stack);
        world.summonEntity(item);
    }
}

12 minutes ago, ZygZagGaming said:

ServerWorld world = (ServerWorld) event.getEntity().world;

I'm going to guess the crash report says 'cannot cast ServerWorld to ClientWorld' or something like that. You need to check if you are on the correct side. Otherwise, it's a blind cast and will throw errors.