The Mastiff is the second legendary rifle in the game. Its performance is far beyond other weapons, and it can cause as much as 288 damage in one shot so that it can make a real punch. The bad news is that it comes with unique ammo. This means you have only 20 shots with it. Still, it is a good pick because, with the right tactic and decent aiming, the Mastiff can definitely bring you the desired victory.
See Mastiff Shotgun in action