A critical hit is a devastating attack that generates more damage than normal. Non-player characters are always subject to critical hits (unless immune), but player characters are only subject to critical hits at the "hardcore" and higher difficulty setting.
Process[]
Every weapon has a critical rating (e.g. "19-20/x2") consisting of a threat range and a critical multiplier. (In the cases where the threat range is 20, it is often omitted from the rating.) When an attack roll is successful and within the threat range, a threat roll is made. If the threat roll succeeds, the hit is critical, and damage is rolled a number of times equal to the multiplier. All bonuses to damage not specifically excluded from critical hits are added once per damage roll. Examples of sources of damage excluded from critical hits are sneak attacks and on-hit properties.
Some creatures have immunity to critical hits, and against these creatures damage is rolled only once, regardless of the threat roll. (If the threat roll was successful against such a creature, a message indicating the immunity will appear in the attacker's combat log.) Creatures typically immune to critical hits include constructs, elementals, undead, and pale masters.
Modifiers[]
Several feats modify critical hits.
- Improved critical increases the threat range.
- Overwhelming critical gives extra damage upon a critical hit.
- Devastating critical kills the target instantly if it fails a fortitude save.
- Ki critical increases the threat range (weapon master only).
- Increased multiplier increases the critical multiplier (weapon master only).
- Thundering rage gives extra damage on a critical hit (barbarian only).
Some item properties modify critical hits.
- The keen item property increases the threat range of the weapon. (This property can be added to slashing melee weapons by the keen edge spell.)
- The massive critical item property gives extra damage upon a critical hit.
All of the above properties and feats stack, with the exception of thundering rage and massive critical.
Touch attacks[]
Touch attack critical hits prove an exception. They are not blocked by immunity to critical hits, and instead of the standard damage and modifications, they use scripted commands. They are also not bound to deal more damage than a normal hit. Some, like inflict minor wounds, will be indistinguishable from a touch attack hit, while others, like the inflict wounds ray, will add a negative side effect.