Berserker Stance increases Nazgrim's damage done and damage taken by 25%. While in this stance, Nazgrim does not generate Rage every second, but the Rage his abilities generate is doubled.
Defensive Stance reduces Nazgrim's damage taken by 10%, and causes him to gain 3 Rage every time he is attacked (but at most once per second). Attacks made on the boss by the tanks do not cause him to generate Rage.
DO NOT ATTACK the boss during DEFENSIVE STANCE, except for tank that has Sundering Blowdebuff.(haha how many times have we heard that)