The final boss on Ninja Gaiden 2 on the hardest difficulty. I may have just sucked but that guy kicked my tail. I think Emerald weapon from FF7 is a tough one as well.

And lets not forget bosses we are supposed to loose to but since I've leveled up I can put up a fight. Use all your stuff and finally loose and expletives start flying when a cut scene takes place and the game continues.

Tekken 5 Jinpachi Mishima:

I would have to say the final boss of Kung Fu for the NES. Of course I was probably 8 at the time, but man, it was killer.

Last boss in Suikoden 1 & 2.

Demi-Fiend from SMT: Digital Devil Saga and Satan from SMT: Digital Devil Saga 2.

radec in kz2 on extreme...fml.

There is some boss in Metroid Prime 2 that you have to fit in Morph Ball form. The entire fight takes place in this goo that continuously hurts you. I hate that boss.

well, I dont remember how I killed Asura ... perhaps I got a good weapon for her ... it was hard to not so hard

I always have the impression that all boss needed 2 fold more HP to make the game more "funny"

I just know the final boss was a good joke in term of difficulty

that the only thing I didnt like in the game : the end is easier than the start

1st golem boss, 1st "haunted armor boss", 1st fire elemental boss were more difficult to me than the last fire elemental boss : good joke
same go for each elemental/boss type

the game was still outstanding

You mean Amorbis? I hated that fight more because of the nuisance of having to be in contact to the atmosphere of Dark Agon more than the actuall difficulty, especially because you'd only get the Dark Suit (which made you suffer less damage from the atmosphere) only after you defeated Amorbis >_<

In Metroid Prime 2, I guess that the hardest fights overall were Emperor Ing and the Boost Guardian in Dark Agon too. 

My manager at Cub's Food.