Keep medium distance from him and watch for his hand gestures that signal ground attacks coming. Your best bet is dodging through these with Cloud Step or other movement skills you've got. When he does his blade combo or that jumping spike attack just stay away or dodge through depending on what feels right The three-hit arm combo is pretty common, and youll want to dodge towards him to avoid getting caught by the range.

Start the fight using Immobilize with A Pluck of Many right away since your duplicates can take almost half his health if you stay aggressive. After that just play defensive until Immobilize comes back up, and hit him with it whenever hes on the ground for free damage.

The Weavers Needle vessel helps a lot here, and save your transformation until hes down to about quarter health for maximum effect. Maybe interesting that you can build Focus Points really well by perfect dodging when hes super aggressive instead of trying to force damage windows.

The real key is pushing him into new phases before he gets through all his attack patterns, so manage those Focus Points and time your transformation right to break his stance. Cloud Step works great to interrupt him when you need some breathing room, but dont get too defensive or the fight drags on forever. If you get the timing down on perfect dodges youll see way more chances to deal damage, and thats what makes the difference between winning and losing this one.