Sneak Attack (+2d6) (NWN)

Specifics
Whenever the character makes a successful attack against an opponent who is flat-footed, cannot see them, or who is in combat with someone else, the character's blow delivers extra damage. This extra damage is +1d6 at 1st level and an additional +1d6 every two levels thereafter. This extra damage is not multiplied in the case of a critical hit.