I just defeated Great Shinobi Owl on my first try and it was way too easy. I was literally waiting for him to rise again for the third phase but he didn't.
After I took the Mortal Blade everything has become so easier and the enemies aren't even that strong. To name a few other than owl, Corrupted Monk, Folding screen monkeys, Headless Ape, Mist Noble, O-Rin of water, Shichimen Warrior, Snake Eyes Shigaragi, another drunkard (I forgot his name) and several lone shadows.
Most of them took just a few hits with the mortal blade and occasionally a distraction with either puppeteer ninjutsu or that Bell that confuses animals between friend and foe. Folding screen monkeys was a beautiful concept but was too easy imo.
The last time I was struck for a while was on that bridge fighting the armored warrior. I didn't know I had to push him off I just kept giving deathblows.
The last good Boss was Guardian Ape. That took a while but after the difficulty took a serious hit. Enemies now have a limited movesets and can easily be blocked/parried. Take Great Shinobi Owl for example.
First move – He hits twice with sword after jumping. Block/Parry and use mortal twice. 20-25% health goes away.
Second/Third move- He throws poison/smoke bomb. Side Jump once or twice and then again use mortal draw twice. Again 20-25% health goes away.
Fourth move- He throws shuriken and then hits. Block and use Mortal Draw.
Fifth move – He uses series slashes. Block/Parry and use mortal draw.
In the second phase. His moves are almost same with changes here and there but overall same strategy.
Mini bosses are worse. They are just regular enemies with more vitality. O-Rin of water for example, two movesets with one special move that can be avoided with simple jump or by stepping back.
So my question is when does it become difficult again ?