The fourth boss is a serious pain, and to my knowledge there hasn't been a foolproof method found of beating him. The best way I've seen/used is to lure the boss back until he won't walk to the left anymore. Walk back to the right and he should conjure a double behind you. If the wizard and his double match your movements as you walk to the right after that, you're in business (and if I remember he does so quite often, if not 100%). Dodge what they throw at you as you walk to the right, and when you've pinned the right wizard against the stairs you can kneel and punch quickly. He disappears and reappears, but he can't go anywhere because of the stairs so he's dead in a few seconds.(posted 9153 days ago)As you noted, kicking off their heads does nothing to them. You have to use low attacks to damage this particular boss. This method is hardly foolproof, but it works often enough to be better than rushing in and attacking. Hope it helps.
Cheers, Brian McLean