Meh I never understood the difficulty in bosses. If you can't win, then your not using enough force. If your still not winninglevel up...then use more force....if you still can't win, equip that item that gives 2X magic (Gem Box I think, dunno been a while) and just spam Ultima till they die.

Simple and easy.

Or just do my all time favorite, Offering and Genji Glove.