What Is Fierce Blow
Fierce blow is a special move that may occur during any Boss fight. Every 3 seconds, the Boss has a 33% chance to cast Fierce Blow. This will replace their next Auto-Attack. Each time the boss fails to use Fierce Blow increases the chance the that the next Auto-Attack (after 3 seconds) will be a Fierce Blow by 33% each time, up to a Maximum of 100%. Once successfully cast, Fierce Blow's chance resets back to 0%.
When cast, Fierce Blow will bypass 50% of any Absorb effect on a Target. This means that their Auto-Attack will do 50% damage to you and the other 50% to the Absorb. Furthermore, as the Boss is striking with all their might, the Fierce Blow cannot be Blocked, Dodged or Parried.
Uniquely, Fierce Blows may be staggered by 15%, instead of the Normal 30%. Read below for Stagger.
What Is Stagger
Stagger is a passive effect that is gained upon reaching Three Talent points in the Arms Warrior Talent "Tactical Mastery". What it does is distribute 30% (15% if a Fierce Blow) of the Damage you take if it deals 10% or more of your Maximum HP, over 10 seconds. This talent, however, does not Work against other Players.
This can be useful when taking large amounts of damage, giving you or your Healer the chance to heal the damage that would have otherwise killed you. It can also allow for more risky plays as a Tank, taking attacks that would normally be too much for any one else.