Soldner-X: Himmelssturmer

This boss is easy once you figure out how to damage it. The boss rotates around and has three blades that you have to avoid. In between the blades is an eye that you have to shoot when it opens. The Flamethrower is the best weapon to use on it. If you get close enough to the eye, you can pass through the blades. Eventually, the boss will rotate faster and faster until it starts to suck you in. Try your best to pull away from it and shoot at the eye to stop the rotations.