I think it would be cool if there were powers for boss battles that would be used in specific situations.
Such as when they are close to not beating the boss, are certain they have the right answer, or are certain they don't have the right answer.
Possible powers could be:
Mighty Swing: guarantees a critical hit if you answer correctly
Magic Barrier: guarantees a miss if you answer incorrectly
Magic Armor: halves damage if the boss hits you (once per boss battle)
I would imagine the mana cost would be high so that they couldn't do this too often.