This is a really fun boss fight but much more difficult than any%. This is also a UV-Max run because I grab the secret and kill all enemies.

The boss deals massive damage with all his attacks so I try to use him as much as possible to take out the other enemies. I start with 12 shots with the holy relic and then run back to try and grab the fairy and group up the enemies. (Fairy gives you 12 ammo) If you get the boss positioned right he can take out the skeletons in one attack which can save you a ton of ammo. The skeletons spawn a bunch of eyeballs which are like lost souls except they also revive enemies so minimizing the amount of them is key.

I get a little lucky having boss infight after second skeleton giving me time to mop up the rest of the enemies. Once it's 1 vs 1 it's not too hard to get the patterns down and land most shots.