The best thin to do when you fight him is to get up to the second level while he still has his legs attached but after that go down and take out ur shot gun and shoot him down from swinging around and then when he jumps back shoot him again
then eventually he will die

p.s. make sure u have alot of ammo and also get the Red9 pistol cuz after you tune it up all the way and then get the exclusive for it, it then become the most powerful pistol in the game