You almost
have to avoid all (or most) of his attacks to win, as he does 2 masks of damage per hit with his mace (the falling rocks still only do 1 though).
He's got ~1,260 health, so the fight will take a bit of time.
I found that trying to heal during the fight simply doesn't work since he attacks fairly fast, so you'd want to maximize damage output.
Equipping Unbreakable (or Fragile) Strength helps a lot, as does Quicknail.
Having the Pure Nail is great too, as with Strength the damage because 31 per hit.
Since you can't get a lot of Soul during the fight, you'd want to do a more nail-focused build.
Using Cyclone Slash while he's staggered is a great damage sink, and should give you ~27 - 30 Soul if positioned properly.
*** Spoiler - click to reveal ***The Nailmaster's Glory charm will help a lot since it reduces the charge time of all the arts to 0.75 seconds (base is 1.35), and only costs 1 notch.
You can use the Dream Nail while he's staggered to gain 33 Soul (enough for one spell or heal). Dream Wielder doubles this, and makes the collection process faster since it gives a massive boost to the Dream Nail speed (0.9s vs 2.4s without it).
Defeating him will award you with 300 Essence, and this achievement when done for the first time.
Finally - as with all bosses - memorizing the attack pattern (or at least knowing the various attacks and their telegraphs) helps greatly since it lets you plan ahead.