Hardest boss?
Mishaela from Shining Force.
you fight through her minions, you get to the bottleneck leading up to here, you get her surrounded and start pounding on her... then she casts level 2 bolt and takes half the life from about 10 members of your party.
Of course, you have plenty of others, but then she starts whacking people around for 1/4 health a pop.
Funny thing is, she only has about 60 health.
Man, what a bitch