Yeah, Hades is not undead, he's a demon. So Devil Killer and Holy attacks works well on him.

Yeah, if you know the right tactics, Ozma is very easy even at level 1. But so is almost every boss in all games. It's just a matter of experiencing the game on your own, without outside interference, atleast the first time through. All I have to say about you guys who slammed both Hades' and Ozma's asses the first time through, and thought they were easy... you got lucky. I had devilish problems with both of them. Beating a boss that is challenging to you is much more satisfying.