Great Shinobi Owl is a boss found at the top of the Ashina Castle in Sekiro: Shadows Die Twice.
You’ll find Great Shinobi Owl at the top of the Ashina Castle on your second visit to the region after you’ve defeated the Corrupted Monk. He’s found in the same place that you fought Genichiro Ashina earlier on in the game, and you’ll only have to fight him if you decide to side with Lord Kuro. Don’t worry, he may look tough, but you’re tougher, stronger, and vastly experienced at this point in the game, so you should beat him quite easily as long as you display some patience.
Great Shinobi Owl hits very hard and will do a lot of damage to your Posture, so it may be a good idea to use a Gokan’s Sugar or two during this fight to make it a bit easier for yourself. The majority of this fight is going to be spent Deflecting, because it’s only worth even considering to attack when you know it’s safe. There are only two instances when you should attack in my opinion, which I’ll get to in a little while, but first let me talk to you about some occasions when you’ll be tempted to attack but you absolutely shouldn’t.
Owl often performs a combo of strikes (which you can see below) that you need to Deflect, and it takes him a slight second to recover from the combo once he’s finished. It’s tempting to go for a hit of your own here but you shouldn’t, as he will go back on the attack very quickly and he’s already filled your Posture bar a fair amount. Instead, use this slight moment of respite to back off and let your Posture bar recover a bit.
He’ll also Perform a massive charging swipe attack that can be Deflected but causes massive Posture damage. He’ll either perform this on its own (watch for when he’s charging at you) or at the end of a combo, such as the one shown below. When he hits the running swipe he stands still for a brief second while he recovers, which may make you think that you have an opportunity to get a hit in, but you don’t. The impact of the attack has knocked you back and it’ll take you a second to recover too, so your window of opportunity is lost. Instead of attacking, just sprint out of the way and recover some Posture, and then get ready for the next attack.
The two opportunities to attack are pretty distinctive and easy to spot. The first is when Owl stops to toss an anti-healing grenade on to the floor. When he does this he’s vulnerable to attack for a good couple of seconds, so we have a perfect opportunity to get a hit in. When you see him stop and toss the grenade, Step Dodge around him twice to avoid the effects of the grenade and hit him once, then back away and wait for the next attack. Don’t get greedy and try for more than one hit or you’ll get punished, just hit him the once and back away. If you get caught in the smoke from the grenade then you won’t be able to heal for a minute, which isn’t a good position to be in during this fight, so avoid it at all costs.
The second opportunity to attack comes when Owl jumps backwards away from you. When he does this, he’ll throw two shurikens at you which you can Deflect (he’ll jump and throw these at various points during the fight, usually following a kick, so watch out for them and Deflect accordingly), and then he’ll jump forwards and perform a front flip before slamming his sword down in front of him. When he jumps forwards, Step Dodge once to the side and you’ll avoid the attack, and you’ll have an opportunity to get a hit of your own in again. Once again, do not get greedy or you’ll get punished, just get your single hit in and back away.
If you need to heal or regain Posture at any point then these windows of opportunity are you perfect moments. Sacrifice your opportunity of attack and use it as an opportunity to either heal or give your Posture bar a break if you need to.
Keep patient and pick away at his Vitality and you’ll eventually break his Posture with your Deflects and open him up for the first Deathblow.
When you hit the first Deathblow, Owl will lay on the floor pleading for his life. When you approach him he’ll pop a smoke bomb and disappear, but he’s about to come back at you out of nowhere, so keep moving and move the camera around to try and target him until you lock on so that you can block his incoming surprise attack. He’ll drop this smoke bomb and come at you several times during the second phase, but once you’ve worked it out once it’s pretty easy to adapt to.
Other than that the second phase is practically the same as the first, although he does have one extra trick up his sleeve. In the second phase, Owl will follow up his kick attack by throwing Poison at you rather than shurikens, so make sure to get ready to dodge backwards to avoid it. The poison will linger on the floor for a short while, so be careful not to step in it while you’re dodging around him or you’ll quickly fill your Poison bar. If you do get inflicted by Poison make sure you use an Antidote Powder to get rid of the effects, but try and do it when you have a good window of opportunity.
Other than that just keep following the tips from the first phase and be patient with your attacks and you’ll eventually wear him down enough to break his Posture and hit the second Deathblow. You’ll have to hit him twice during the final Deathblow, so pay attention and don’t miss your prompts.
Killing him well earn you Memory: Great Shinobi, which you can use at a Sculptor’s Idol to permanently increase your Attack Power, and the Aromatic Branch, as well as a big chunk of experience points.