In the boss battle with Bitoriz Mendez there are two levels bottom floor and top floor. Start off by going straight to the ladder. Climb it and go to the left. There are some boards that are blocking the way of the middle of the place you are fighting. Get behind these boards and look down, now while Mendez is in his first form he will just be walking looking up and walking at you but hes walking towards the wall. Now if you would like to finish him off quickly just shoot him with the shotgun or rifle. If you want to conserve ammo just use your pistol. Now in Mendezes second form its a bit more tricky but its possible. Make sure that Mendez is on your left of the boards and your in the right corner and if positioned right he will extend his claw and try to hit you but fail and he will continue to do this like a glitch. Same as the other way if you would like to finish him off quickly then shoot shotgun shells or rifle at him. Or to conserve ammo just finish him off with your handgun. Get your reward when your done.