Monster Swarm

This is version without config yet. Just ported it. Config might come later if I find time and will to work on it.

Reasonable default:

Monsters target you from far away at all times.
Zombies/Skeletons can digg only underground (below 40) in overworld

in other worlds they can digg everywhere.

So you are safe in your base on the surface in the overworld, but anywhere else is dangerous.