who's the hardest enemy that you've encountered in any of the AC series?

[NiX]

Shouldn't this be in AC Stuff? Anyway, the mods will come along.

For me, the most challenging (read: cheap) AIs can be found in the Master Arena of MOA. >_<

Ace, the 1st Ranker of AC3's Arena is also memorably challenging.

Oh, and the baddies in AC2AA's Lost Field were pretty hard too!

EDIT: Oh wait, how could I forget that giant MT in AC2. >_< That bastard took me countless tries to beat.