Berserk

Barbarians have the ability to drive themselves into a mindless frenzy, a state known as berserking. It is easier to do so while already hurt or fighting. This ability provides a significant bonus to both the user's hitroll and damroll, and penalizes his armour class. While anyone in a berserker rage is unable to clearly identify how wounded he is, his hit points may go into the negative while in this state.