They made Chaos much harder in DoS. He has 20,000 HP and his attacks are more accurate. You'd be better off replacing a Ninja with a master because by this time your master can do a barehanded attack that does 1000+ damage. Cast Protera and Invisira on everyone, then have your black mage cast NUKE (I refuse to call it flare) on him.

Also, give your Knight the Masamune and let your white wizard cast holy alot.