Npc mobs that does stuff like looks for stuff it needs, mining, crafting, talking, building houses in randomly with furnitures, using tools, and do things it needs to do, and so much more
You have to be attentive for a big amount of enimies & monsters, one more odd & powerfull then the other. some mobs are as powerfull as they can completely ruin large areas, be carefull with them!
The most mobs is workinng in teams, you can also change to theirs team. There are also spawning some (generated) buildings, like big underground-lab, forts and massive pyramids ...and weather & a lot of misc stuff
some extra info
call bots like: come and come or rightclick them
they can aslo buy things using smartshop
make them to a guard: right click a npc with a diamond, this makes them stay around the position. useful to keep monsters and enemies away.