Hadern's last boss fight from Mortal Shell. So for this game which I mentioned earlier, to unlock a new weapon you have to beat a mirror match styled boss called Hadern for each weapon. This is fine. Once you collect all the weapons and shells (pretty easy and possible to do early without going into any of the dungeons) you can fight him one more time at the hub. This is where bullshit starts.
So he's now a boss with 2 phases and 2 health bars, one where he dual wields katanas, another where he uses an axe, nothing special for souls like games. No, what makes it bullshit is the I-frames he has on his dodges in form 2 with the axe. He can and will dodge out of every attack he does. If you stand there and harden to block an attack and then attack, the short lag between you unhardening and you attacking is enough for him to dodge, and he does this every, single, time. The only consistent attack that lands is the sprinting jump attack after you block an attack.
What's that? Just parry him? Good luck. There are unparryable attacks in this game. His unparryable attacks in his second form are both fast enough to be hard to react to, but also slow enough that you can't parry spam. He can attack in a 3 or 4 string and some of those are unparryable, some of those are parryable. He, like you, can also harden, which means that he freezes mid animation, turning to stone and can block one attack, before unfreezing and continuing the animation. Thought you had the timing down? Too bad. Just wait till he unfreezes to parry? Turns out the attack is an unparryable. Just trade with him bro? He hits much harder, so each trade is a loss.
There are fast bosses in souls borne games, and then there is this. He is impossible to hit clean unless you get the parry, which is hard as hell. Just... Annoying to fight.
Edit: Finally killed this fucker using the lamest strategy possible. Use the low heath-high stamina shell, equip the very long Martyr's Blade, use the strong - light - light chain from far enough away to poke at him without letting him get close, where I am just outside the range where he normally reacts to the attacks with a dodge, or if he does backstep, the light attack thrusts still poke him.
It's been a very long time since I've had to cheese a souls like boss. This was one. I also discovered he had a really annoying, bullshit attack in his first dual katana form. He holds one reverse grip, the other forwards. One of his strings start with him quickly winding up for an attack with the forward facing katana, at the same frame, he brings the reverse grip with it, which hits you. It's literally unreactable. I have swung at him with the speed weapon in previous attempts, be about halfway through the attack animation, and that reverse sword swing starts and hits first. I don't think I have seen a more cheap attack in a soulsborne game before.