We need strategy guides for this.

When you say "perfect form" are you referring to the one in Realization? I just updated the strategy for that one.

The way I did it was to die until he's at 25% hp where he will begin using soul absorption, then summon a pet, have said pet attack him while you spam the shadow that is summoned. Repeat the pet spam each time he uses soul absorption and eventually you'll kill him.