Critical Strike

Critical strike is a passive ability that gives a chance to deal bonus damage on a successful attack.

Mechanics
Critical strike is defined by two values: the critical chance and the critical damage multiplier.

Critical damage is physical damage and is reduced by various types of armor. When a critical strike triggers, the unit's attack damage number visible in the HUD gets multiplied by the critical strike's factor. The result of this multiplication shows up as a red number above the target if the attack successfully hits it. This means that the red number displays the damage before any kind of damage reduction or amplification the attack target has. This also goes for illusions. The red number shows the result of the illusion's attack damage multiplied by the factor, before it gets reduced by the illusion's outgoing damage reduction and armor. Critical strike does not work against buildings, and only very few work against wards. Because critical strike multiplies the attack damage of a unit, after attack damage modifiers, it is a scaling ability (unlike the damage of 's mini-bash ability).

All critical strikes are subject to pseudo-random distribution.

A ranged critical strike is calculated on projectile ejection rather than on impact. For example a unit which already lost the debuff on impact, still gets struck by critical hit.

Stacking
Multiple critical strike abilities do not independently stack, as they cannot trigger on the same hit.

Interaction with other passive abilities

 * Lifesteal: Lifesteal is calculated after critical strikes, which means that it increases the amount of life you steal.
 * Cleave: Cleave is calculated after critical strikes, which means it deals increased damage to all units within the cleave radius.
 * Bash: Bashes and critical strikes can proc on the same attack, and are never multiplied.
 * Illusions: Illusions can use the critical strike ability (red critical numbers are before illusion and armor reduction). Pseudo-critical strikes cannot be used by illusions.

Other sources
The following abilities involve a critical strike mechanic, although they are not triggered as a chance on attack.