This boss has two attacks. The first shoots numerous balls in a stream. These balls do little damage. The second attack will be rings of balls that should be avoided. As soon as the level starts run there the spear trap and jump on the left edge of platform to the right of the boss. Press the square (attack) and x (jump) buttons repeatedly continuing through the fireball stream attack. Break off your attack before the ring fireball attack. Jump down and head toward the right corner. This will give you room to avoid this attack. Return to attack platform and repeat.