So in my plugin I have mob regions. A region has a constant number of spawned mobs (such as 4 zombies), which are tracked by a hashmap. The problem: Mobs de-spawn when there are no players within 128 blocks of them. I need to remove mobs from the tracking hashmap when they despawn. How can I do this? Before you suggest ChunkUnloadEvent - this doesn't work because mobs usually despawn BEFORE the chunk they're in unloads.