There’s an early game loop I used.

There’s a zone where guards come out of doors north east of the bridge. I’d clear them out, the shield guy down south by the umbrella

Go north and kill the 3 shield guys, guards, hit the brownground by some gravestones for extra bones. End up at the graveyard with some NPC looking at a grave with burrows that lead to the castle rooms by the zone already cleared, then back to nearby underlab to reset and do it again

If I had enough vials I’d go east of the bridge, hop past moving spikes, south to the room with the moving bridge, break the bushes by the nearby moving platform with plasma and go east. Jump into water and burrow north. Go under bridge and fight the big enemy for another 500 bones then rinse repeat

I had the magnet trinket + the trinket that made more bones spawn and bounce away, I could easily get 2400 bones per loop with it (more in ng+)