In the newly added spartan ops mode from halo 4 there is a mission called Shootout in Valhala (Episode 3 - chapter 4) in this mission you'll activate some turrets before receiving a Mantis mech and go up against 14 hunters fairly early into the mission. Simply tear them up with the mantis (not so tough when it's you who now has a cannon strapped to your wrist) save and quit and then rinse and repeat.
Also bonus side note, there is an Easter egg on this mission, right at the start look to the row of pine trees to your right and shoot the brown box at the top. Plays some amusing dialogue from the Roosterteeth show Red vs Blue