After recently completing Sekiro and the original Dark Souls a while before that, I am very familiar with FromSoft tough-ass boss fights.
My own personal boss fight nightmare, was none other than Ornstein and Smough (O&S) on the original Dark Souls. I would have to look back in the Souls thread, but it took me several reinstalls of the game and literally years of trying, to finally beat these two.
When I did eventually defeat O&S, the waves of euphoria almost brought me to tears of unbridled joy. After literally hundreds of attempts, the sight of the words "VICTORY ACHIEVED" will forever be etched into my gaming memory banks. Yeah, I know this sounds overdramatic, but I will honestly never forget beating O&S for the first time.
Honoury mentioned to Father Gascoigne in Bloodborne. He was an absolute devil of an early-game boss. Let us not forget The Valkyrie Queen and Gna in the last two editions of God Of War. They were both total bitches to fight.
Sekiro bosses, Glock Saint, Geni, Owl Father, and Demon Of Hatred were all very tough Mofos, but none of them got me to the levels of frustration and despair as O&S did.
SO...
Who was/is your boss nemesis? or which old foes do you love revisiting to renew old acquaintances?
Or perhaps, your fav boss was a pushover but just so much fun to fight?