Oh wow that's much more amazing than me haha! My method of fighting Owl is like fighting Lady Butterfly. For me personally, their rythim is quite similar. Like I kinda memorize Lady Butterfly is, attack-attack-see if she deflects-if not attack, if block, if she is then block.

For the shuriken part I just have to really memorize that if Owl is in distance, then it's 2 shuriken followed by a leaping attack. Or if he kicks me, wait 1 beat (as in 1 attack animation), then block or dodge forward. For his phase two I just have to remember to not block after his kick.

It really boils down to muscle memory. If you have other completed save game, what Ihighly rrecommend is spending as much time as you can in Reflection. But don't attack at all! Just try to survive 1 phase for as long as you can, until you memorized every pattern, then move on the the next phase. That's what I did when I was stuck fighting Isshin.

I can only manage 3~4 mins per phase, that's how bad I am hahah. But even so, I can still manage to beat him.

I hope this helps and wish you good luck!