Freakin Wesker... I certainly spent the most TIME trying to kill wesker with my dad, we couldn't figure that bastard out forever. But Definitely Yiazmat was the longest (although it seems like a cop out answer) and next I probably spent more time on Zodiark in FF12 than Hellwyrm. It was very much a plick away at its health slowly trying not to die and recovering from near party wipes.
Honorable mention goes to The behemoth boss thing in Resident Evil 5 (fought from the stationary Humvee) on co-op on Professional difficulty... Getting two people to not mess up the fraction of a second window to not get wrecked was tough enough but getting enough damage in the right spots the whole fight AND still not messing up timing... brutal. Had 256 deaths on it before we won.
Bookmarks