I know the rules of spawning, right now i have built a box with no ceiling further underground to semi-automatically farm them. (This box is around 1000 blocks long so the pillar will always spawn roughly in the center of it) I only have one of these boxes so far and the farming mechanic is not complete, but here is my plans for what will happen when i am finished:
1. teleporter to the farm
2. teleporters off screen to send spawned pillar enemies to the center, where I can kill them with either a stardust dragon or any other weapon that can move through walls and can kill them fast enough.
3. banners for enemies that can move through blocks so i can kill them faster than they kill me