@Asteroid Dungeons:
- Derelict Spaceships: large structures made of tin or something, with remains of (non-functional) thrusters and stuff, maybe with some occasional oxygen sealer somewhere in the floor. Large holes in the walls with asteroid stone blocks lying around. Small floating sentry drones shoot laser beams at you. The boss could be either a large security robot or some kind of an giant space creature which took residence in the wreck.
- Giant space creature nest: like the large asteroid worms in star wars, it's a big asteroid with some... thing inside. The weaker mobs on the way to it should be smaller versions of it, it's spawn or something
Other stuff which could be added:
- Half-broken "wild" astrominers which occasionally attack you
- Evolved Ghasts
- Pieces of the Overworld floating around, like broken off by asteroid impacts. With a layer of dead grass and dead trees on top. Maybe rotated, so that the trees point horizontally
- if AE2 is present, intact versions of it's black meteors with the chests inside