The Devil May Cry series is really hard. Unless you play on the easiest level (which I refuse to do, despite the fact that I can't get past one of the bosses in 3).
The Twin Armors I presume, since almost everyone I know gets stuck on them.
Surprisingly not. It's the boss at around level 18/19. Can't remember his name, just that he was ridiculously impossible.
I can't remember which one that is... The monster who is blind or the shadow clone maybe? Well, that games bosses are pretty nasty...