Ring of Pain

Easiest way: Hermit's Tiara and Spiritual Mask. Ignore Attack stat boosts and focus on defense and speed. gather souls and use them on legendary mimic to get Soul Cannon Spellbook.
before reaching the owl, make sure you've got decent amount of souls for the spell book. the battle itself is quite simple, just go forward to the owl, cast the spell and step back.

So not a direct guide but will perhaps save someone a run that’s going well. This also applies to scrolls, you cannot use them if they don’t align to the set. I stupidly threw a run but using a legendary scroll at the end whilst going for the brute set achievement.