Easy boss because he has only two attack patterns, never moves and does minimal damage.
Jump on the small platform to the right of him at the start of the fight (you will take damage from the pit). Attack him between waves and he'll die fast. Run to the right during each attack to avoid the fireballs without trouble. The first pattern is similar to the small eyes. He fires at your direction. The second pattern is a cirlce one and can easily be avoided.