I think it’s getting those maggot worms in hell tide to spawn. I just can’t reliably get them to spawn frequently. Sometimes it’ll be 2 in 30 seconds, then I don’t see them again for 10 minutes
I think they spawn 1 or 2 times in the each threat level cycle. I guess it's the fastest way to lvl up on higher levels because those xp bubbles scale and you are getting multiple, you can easily go through the cycles by doing spires, opening lesser chests and farming maiden.