My strat for him was put him to sleep then mana drain him before he changes phases so he can't use three slashes. That leaves him with splash blood and his agi buff. Splash blood does like 90% hp damage + some extra maybe so it can't kill you and his agi buff will at worst let him keep up with you if you have the agi soft cap. Also his ai is programmed to always dispel requiem so if you have an extra action you can invalidate his next turn by using it.Welp, never mind. Just found out that Drake Sword plus oil absolutely destroys him. He sure gave me trouble tho.