I fought the Fume Knight for 5+ hours yesterday.

Not sure how many times I actually died against him, maybe 80-90?

Started around 6pm while just playing..took a short break to go out somewhere (left game on)

Finally beat him at around 11:48pm ish

I never had anywhere near the trouble on any other boss than this guy; I had fought the Smelter Demon an hour before and it took me around 6-7 tries.

He just kept destroying me on his second phase, doing 80% of my HP in a strike

I got him down to under ~10%hp around 13 times and he managed to kill me every time...everytime. Even that time he bugged out and didnt go into his second phase until he had 25% HP left - I went ham on him and he jumped on me for 80% hp ruining that attempt.

His AI is incredible, felt like I was fighting a person most of the time. He actually reacts at a split moment if you try to drink an Estus even if he is half the screen away you will die.

edit: Sinh the Dragon/Ancient Dragon only took me about 9 tries.