So I decided to sit down for an afternoon and just master him, finally. Derp around with some weapons and ended up with some interesting findings:
- if he starts to summon enemies, you can use XX>XYYY with the Claws (Vermillion Bird), this forces him to block and he'll cancel the summon. Great for single-segment runs where his summon can mean death.
- if he's hovering in the air, use the RT button to unlock the lock-on. For some bizarre reason he'll stop flying around and his next move will nearly always be the ground-pound that lands him. Be sure to lock-on again immediately after to not die.
- XX>XYYY with the Claws (Vermillion Bird) seems to be the best punish paired with YYY (Undefeatable Demon) with the True Dragon Sword whose damage buff works great here. Undefeatable Demon is safer by a large margin, but Vermillion Bird has a unique quirk. If you do it after he grabs, he'll always try to grab you again, which gets him stuck in some sort of loop of grabbing you. This is helped by, for some mysterious reason, you're completely immune to grabs for nearly a whole second after landing from Vermillion Bird. The game apparently thinks you're still airborne?
- he's...surprisingly vulnerable to water-running moves which deal massive stagger to him.
This allowed me to absolutely melt Zed in around 15 seconds:
I've been able to get this killspeed nearly consistently, very rarely the lock-on trick won't work though.
You can see the throw-invulnerability near the end. My musclememory really wrecked me there at the start, making me dodge away.
Enfin, thought I'd share! Hope this helps other ninjas!