The Mauler is a Boomer Class enemy with a shield and an explosive tip flail. The Mauler can be one of the trickiest enemies because he has exceptional health, good defenses and an impenetrable shield. If you attack him, he'll hide behind his shield until you relent or until he gets close enough to attack.
At this point, you need to either hit the shield with a One-Shot (which will punch through and kill him), shoot his exposed foot under the shield or try to flank him so that you get behind his shield. If you can get him in between several people, he'll fall pretty easily but you can also set a flank up yourself. If there is only way way to get to where you are and you can get along side that path, you can shoot behind his shield because he always has to have the shield in the direction he is moving.
