Odin Sphere; any boss. Seriously! This is one of the reasons why I don't wanna play the game anymore. Beautiful graphics, great music, good plot, enjoyable voice acting...and still, the gameplay kills me! You often face enemies that, while they might not be more powerful than you, their attacks have priority over your combos so if you're doing a combo, 1. You can't stop and 2. You're screwed if an enemy decides to attack you halfway through.
Oh, and it's not just boss battles! It's any enemy, even the lame ones! Oh, and there's no grinding in this game. Oh, and if you go to a stage unprepared, well, too bad! Sucks for you because you can't go back and prepare yourself properly, even if you die!
The best "strategy" is: Hit, run, hide, heal, go back and repeat the same process. Really, that's how you win battles. I don't know; it might be just me playing the game wrong...somehow. But there's a difference between a challenging game and an unfair game. if you ask me, Odin Sphere is the latter. It's really a shame.