Helpless Defenders
This describes persons who are sleeping, unconscious or totally paralyzed when attacked. For sleeping creatures, it is assumed that sleeping creatures won't awake because the attacker has succeeded in approaching through stealth.
When an attack occurs, there is no need to roll a d20 to-hit. Damage is automatic. The total damage done will be 10-60% of the creature's maximum hit points above zero, each round of the attack, per attacker.
A thief or assassin may prefer to automatically backstab the opponent or attempt to assassinate. If assassination fails, the damage caused will be 20-70% of the helpless defender's hit points.
For example, a creature with 20 hit points is unconscious when attacked by a non-assassin. The attacker will roll a d6 x 10% x 20, or 2 hit points per pip appearing on the die. In all probability stunning the creature outright. However, since such an attack will wake a sleeping creature, or potentially ruin a paralyzation spell, most defenders will no longer be helpless and will have to be hit thereafter (even if they are stunned, they are still rated according to their armor class!).
In the case of an unconscious character with less than -3 hit points, however, the defender will remain helpless even after taking damage.
Experience is not rewarded for attacking helpless creatures.
See Attacking in Combat