From D&D Wiki
|This material is published under the OGL|
In the standard d20 rules, armor reduces the chance of a character taking damage in combat — but that’s the limit of its protection. In this variant, armor not only protects in that manner, but also turns fatal blows into less-threatening hits. Armored characters are often more easily battered into unconsciousness than brought down by lethal damage. It’s a system that works well in campaigns with a great deal of combat between armored foes, but in which magical healing is not common. It’s also ideal in a world where ethical or legal standards dictate that subduing or capturing opponents is preferable to killing them.
Behind the Curtain: Damage Conversion
With this system, a character still takes as much damage from a hit as in the normal combat rules. Barring any magical healing delivered during the fight, a battle lasts just as long as in a standard game. Since nonlethal damage goes away faster than lethal damage, though, characters can recuperate from their battles relatively quickly, even without magical healing, making this variant ideal for low-magic campaigns.
However, healing spells become potentially doubly effective, since they heal an equal amount of lethal and nonlethal damage.
Nonlethal attacks become less frightening to armored opponents. A fighter in full plate simply has no fear of unarmed opponents, since they have little chance of injuring him. (Of course, they can still overrun, trip, or grapple him, so he’d be wise to keep an eye on them all the same.)
Another effect is that defeated foes remain alive (and unconscious) unless dispatched after the fight. This can decrease character mortality dramatically—since most characters who fall in battle will be merely unconscious, but not dying—but it also introduces the potentially ugly postcombat scene of the characters feeling it necessary to slit the throats of their unconscious foes. Some characters, particulary paladins or other chivalrous types, may suffer serious moral qualms.
This variant is probably best for campaigns in which it’s acceptable for the bad guys to survive a fight. Perhaps a defeated villain’s honor prevents him from returning to plague the heroes at a later date, or maybe the style of your setting rewards characters for defeating opponents without killing them outright (such as in a swashbuckling campaign). Otherwise, characters may feel that they are punished for refusing to murder unconscious foes with regularity, since those enemies will certainly recover from their injuries and vow vengeance against the PCs. Encounters in the campaign may often involve fighting the same opponents again and again, rather than fighting new monsters and opponents.
Armor Damage Conversion
Each time an armor-wearing character is struck by an attack that deals lethal damage, the amount of damage dealt to the character is reduced by an amount equal to the armor bonus (including enhancement) of the armor worn. The character takes an equal amount of nonlethal damage. Damage that is not affected by damage reduction (energy damage and the like) is not converted.
For example, while wearing +1 full plate (total armor bonus +9), a half-orc barbarian is struck by an arrow for 6 points of damage. Since the armor can convert up to 9 points of damage per attack, the entire 6 points is converted from lethal damage to nonlethal damage. The half-orc barbarian's hit point total remains the same, but he increases his nonlethal damage total by 6 points. Later, a hill giant strikes the half-orc barbarian for a whopping 22 points of damage. The armor converts 9 points of this damage to nonlethal damage, but the remaining 13 points are deducted from the half-orc barbarian's hit points.
At your option, you can make natural armor work in the same manner. However, this means that almost no defeated monster is truly dead, which may prove problematic (see Behind the Curtain: Damage Conversion). This rule also interacts strangely with regeneration — since all damage dealt to a creature with regeneration is treated as nonlethal damage, a regenerating creature with armor or natural armor actually takes less damage than normal when using this system. In case of regenerating creatures, consider eliminating the rule that natural armor works in the same manner.