Discuss FromSoftware's Sekiro: Shadows Die Twice
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I'm not sure if this is helpful for anyone, but I found that you can get his first phase down instantly using a yashikura's sugar and mid air mortal draw twice. He sometimes survives but when he does he has one or two hits left before he's down. This leaves you with one phase to deal with and only down one gourd (for the healing once the sugar wears off).
It worked for me. Now I just have to find a way to beat his second phase /:
I can’t figure out how to mid air morta draw. I always just come back to the ground l I don’t stay in the air
You must be talking about the first encounter. This is about the version in Hirata Estate which has more health and a bigger posture bar; or you were playing with hacks. There is absolutely no way just two mortal draws cuts down all of his first phase health even in NG.
Bloody Owl of Hirata
On his regular slash combos, don't counterattack unless he does the double-slash. Instead wait for him to finish the combo, which is usually either the firecrackers which you can run around counterclockwise to hit him in the back, or a sweeping attack which you can jump back-left to land on his head. The extra easy deflects help build up his posture a little faster
His posture bar's size is equal to the size of his beard
Initially I tried to keep away and punish openings like the Greas Shinobi fight. This doesn't work nearly as well because the arena is tighter and the columns get in your way when you try to dodge. It also takes forever.

So instead I learned how to dodge the firecrakers (rotate counterclockwise when it's after the combo or just dash through when he's jumping backwards) and just kept charging him. Almost everything can be deflected fairly easily and if you have a lot of prayer beads the posture damage can be handled (unlike the first fight). Took a few attempts to get a good read on when I should be punishing but when I got past the first phase I also got to the end because the second phase is very similar.
Watching videos of how to beat this boss, all of them from two years ago, I started to think: FS patched the game to be harder. In the videos, players spams attack button, Owl (Father) does nothing. Try to do the same, he jumps, he evades, he kicks your face and says you’re starving. Nine necklaces, he kills me in two hits. YouTube guy, life bar by the half, takes 3 hits in a row, not blocking or deflecting, still alive - no use of any candies or spiritfall. And sometimes Owl stops attacking, he just walks in circles for a while. Never happens on this side: he doesn’t get off me.

It seems like FS noticed gamers were finding different strategies to progress, identifying AI weaknesses and taking some advantages. And then they took it off. If playing aggressively was fun to players at first, now they made Owl more aggressive, breaking their own logic. He has smaller safe windows to hit him and almost all of his attacks can't be evaded - they track you.

Evading and deflecting - basic mechanics of the game - don’t work here, and when I beat him, I don't felt like I "git gud", as you say, I felt it was pure luck.

Don’t get me wrong: Sekiro is a great game, and has some bosses that were very fun to beat, but when the devs fix things just because players are finding it easier than it was planned to be, this is just dishonest.
But imagine if it was your game and you watched a video of your imagined beefed up super ninja dad getting spanked by his black headed stepchild instead of the other way around? Wouldn't you want to beef up your creation so it's more like what you hoped for? Maybe make it so he did some of the attacks you put effort into designing? I mean the dude is supposed to be the man who taught and raised you, except in his prime. Of course it's going to be really hard, it's overcoming the Wolf's entire life
If you have projected force and suzaku's umbrella you can shield yourself from the firecrackers after the shoulder bash, and then hit him with a fire charged umbrella + kusabimaru.