heh, i wouldn't call him hard, beat him without using subtanks.
his second form was predictable as hell. the only thing that even bothered me was getting frozen - and that only happens when i don't pay attention.
and i wouldn't say any RPG boss is hard...unless there's a limitation to experience points, all the bosses are easy, it just takes time.
MMX7, on the other hand...the whole game was just a friggin hassle to deal with...mainly due to poor game design.