Games Hardest Boss you've ever fought in a game?

[Equaling Heaven]

Darklurker was pretty awesome and hard although he is definitely in my top 3 hardest bosses of Dark Souls, I personally found Sir Alonne to be the most difficult to fight because of his speed. And if we include BS bosses, then no one even comes close to the level of BS'ery of Lud and Zallen.

Alone was okay to me because I cheesed but the pets... Yeah.
Me: "hm this area so hard to even cross, I bet the boss will be a bit easier"
Game: "NOPE! AND GET IT DOUBLE BITCH"

 

[Haya-san]

The Nemesis from Resident Evil 3 (PS1 version). You are given the option to flee in most of your encounters with him, but if you decide to fight him, you'll need to save up ammo beforehand and make full use of the dodge technique (which I sucked at when I first played the game). Beating him in the first encounter is an accomplishment, since the shotgun is the most powerful weapon you get at that point, and you might want to save the ammo for when you have to fight him. Even if you decide to flee, there's that creepy stalker background music that plays with your nerves, and then he rushes at you out of nowhere.

 

[Slaynoir]

Top Five for me are:

1. Adamantoise from FF 15 (I went savage for 3 hours just on that guy, and was on a super low level kick throughout the whole game)
2. Orphan's second form from FF 13
3. Gherman, The First Hunter from Bloodbourne (True Ending)
4. Battle Andross from the OG Star Fox 64 (as a kid I got so mad at this guy)
5. Gruntilda from Banjo and Tooie on the 64 (again as a kid)

 

[kakashi919]

Ozma FF 9...stopped playing for months because of that guy.. finally got lucky and beat him when I went back lol