Astral Spikes

They can't be killed, but you can avoid them rather easily as they only slowly cruise around on the ground, lacking any climbing, jumping or flying ability. They can go up short flights of stairs, but not through regular-sized doorways, and they don't seem to be able to take 'big' steps up, as the one in the Turntable area is stuck in the lowest circle of the floor.

Example of:
Invincible Minor Minion