Characters who are already Proficient in a skill, armor or weapon group may choose to gain Expertise in that skill or weapon group instead, when a feat or class feature would grant them Training. Expertise grants an additional +1 Expertise bonus to your check value, in addition to your +2 Training bonus.
- When you make a skill check to perform an extended action using a skill you have Expertise in, you may choose to treat your check value for that extended action as if you had rolled a 10, instead of rolling. If there is no risk associated with failure, you may also choose to take ten times the normal amount of time required to perform an extended action to treat your check value for the extended action as if you had rolled a 20, instead of rolling.
- When you make an attack with a skill or weapon group that you have Expertise in, add your Expertise bonus to your damage, and you achieve a critical hit if your attack check exceeds the targeted defense by 10 or more.
- When you are wearing armor that you have Expertise in, you reduce the armor check penalty for that armor by your Expertise bonus.
- When wearing a shield that you have Expertise in, you gain your Expertise bonus to your cover bonus against opportunity attacks, area attacks and ranged attacks, and reduce the shield check penalty for that shield by your Expertise bonus.
Certain actions, weapons, and armor have the expert only property.
- An action with the 'expert only' property may only be attempted as a stunt if you are trained, and suffers a -5 penalty to your check result. While you attempt the stunt, you grant advantage.
- A weapon with the 'expert only' property may not be effectively wielded by a character who does not have Expertise in any of that weapon's weapon groups. A character may attempt to attack with such a weapon as a standard action, but they may not perform opportunity attacks or gain advantage, and they grant advantage as long as they are wielding the weapon.