use your mouse to move the gun, press down your mouse for bullets to shoot out from the gun. if you hit the boundaries with the gun you lose the boss fight. there are 3 phases once you hit the boss 10 times the boss goes up a phase, each phase goes up in difficulty. if the boss touches the gun you lose the boss fight, but this is only after the boss moves towards the gun.
it is recommended to play in FULLSCREEN. the boss fight looks the best best in fullscreen when the boundaries come in
