Split Int/Faith deletes Dragonlord Placidusax (Elden Ring)

Looking back, I'm actually an idiot. The buff from Lord of Blood's Exultation and the White Mask ran out before casting, but at least I still killed him. I should have used Bloody Slash to trigger Red-Feathered Branchsword. Either way, equipment used was:
Wing of Astel +9
Golden Order Seal +10
Blood Rapier
Lightning Scorpion Charm
Godfrey's Icon
Lord of Blood's Exultation
Old Lord's Talisman
Spellblade Gloves, Trousers and Attire
Wondrous mixture:
Lightning shrouding cracked tear
Stonebarb cracked tear