Beat it. When you know the pattern the skull boss is actually easier in my opinion. His pattern is: Right side of the screen --> Fireballs --> Middle of the screen --> Fireballs --> Left side of the screen --> Fireballs. I stayed at the left until he arrived, then ran to the right side of the screen building up my magic attack. When he is at the right side again, attack him with your magic while you run to the left side of the screen.