Stagger

Stagger is a temporary state of immobility that players can apply to enemies to interrupt their action, typically through attacking, pushing, or using Career Abilities.

General
Each attack for every weapon has its own built-in stagger strength (The 2 Handed Hammer is the highest stagger strength), which is further enhanced by Hero Power and Talents. Enemies can resist staggers based on a combination of the unit's stagger resist and stagger reduction values or during special animations such as climbing. Only certain enemies have stagger reduction, including Marauders, Gors and most Elites. Stagger reduction can change during certain enemy actions, attacks, or combos, notably during the Berserker combos or overhead strikes by Elites. Stagger reduction is ignored by certain attacks (such as 1h axes and 1h sword/falchion finisher attacks) and pushes with shield weapons. Headshots and critical strikes also ignore stagger reduction.

Stagger System
The Winds of Magic update (Patch 2.0.0) introduced the stagger system which made stagger a much more significant combat mechanic, under which staggering enemies (via any source) adds a stacking debuff that increases damage taken. Each stack of stagger increases damage taken by 20%, up to a maximum of 2 stacks. The debuff is cleared when the flinching animation ends. Enemy health values were increased to compensate, scaled with how staggerable the enemy is. Ranged weapons benefit from stagger, but they are unaffected by stagger talents (except by the Bulwark damage buff) and count enemies as having at least 1 stack of stagger.

Stagger Talents
Every career has a row of talents at level 15 which consists of a combination of the following:


 * Assassin: Headshots and critical hits deals bonus damage as if the target has 2 stacks of stagger.
 * Bulwark: Enemies that you stagger take 10% more damage from melee attacks (also effects teammates) for 2 seconds. Deal 20% more damage to staggered enemies. Each hit against a staggered enemy adds another count of stagger. Bonus damage is increased to 40% against enemies afflicted by more than one stagger effect.
 * Mainstay: Deal 40% more damage to staggered enemies. Each hit against a staggered enemy adds another count of stagger. Bonus damage is increased to 60% against enemies afflicted by more than one stagger effect.
 * Smiter: The first target hit receives damage as if it has at least 1 stack of stagger. This works on Monsters and Lords. First target hit refers to the first enemy who receives damage in a given attack -- for example, if there are three unstaggered enemies in front of the player, enemyA/enemyB/enemyC, a cleaving swing from left to right would apply bonus damage to enemyA as if it were already staggered once. However, this does not mean that enemyA is henceforth always treated as staggered as the talent's tooltip suggests. If the player were to wait for the enemies to become unstaggered, and follow up with a cleaving swing, this time from right to left, only enemyC would receive the bonus damage.
 * Enhanced Power: Increases total Hero Power by 7.5% before other buffs are applied.

Here is how the damage bonuses compare:

Tips
The best talent will depend on the hero's weapon and role to a large degree. With single-target oriented weapons like Dual Daggers or Axes, Assassin and Smiter will provide the best value. Heavier, cleave-oriented weapons such as the Two-Handed Hammer or Flail will be able to maximize the value of Mainstay. Bulwark will generally function best on weapons and roles that revolve around staggering enemies, such as Shields on stamina oriented heroes. Enhanced Power is excellent for ranged focused heroes like Waystalker, Ranger Veteran, or Sienna's careers as ranged attacks do not benefit from the stagger talents, and the extra power often allows the hero to reach useful ranged breakpoints.