Okay, yet another damage system, hehe. 
I was inspired to write this up based on some of the house rules cooked up by other contributors to this board. So this is not an attempt to be original, so much as to balance out a mixure of existing ideas for spicing up hit point damage. I will probably play test this system in my next game, but I thought I'd post it here just for fun. So, submitted for your (dis)approval...
The following house rules for damage effects are inspired by the VP/WP damage system used in various d20 games (Star Wars, Wheel of Time), and other house rules posted to the ENWorld boards (primarily by Psion and Hong). The Critical Effect rules in particular are almost entirely the work of Psion, and are used here with only small changes. Thanks for the ideas, folks!
WOUND POINTS
In addition to Hit Points, your character also has a number of wound points (WP) equal to his current Constitution score. These wound points are not a substitute for hit points. HP damage is dealt nomally as specified in the Players Handbook. However, instead of the death threshold being -10 HP, under this rule your character does not die until his hit points have been reduced to a negative number equal to your current wound points.
Wound points may be lost through Ability damage to Constitution, critical hits, or critical effects (see below). Loss of wound points will shrink the 'death cushion' of available negative hit points, as specified above. Additionally, if a character is reduced to zero wound points, death occurs immediately, regardless of how many hit points may remain. Wound points are never less than zero.
Thus, under this house rule, character death occurs under the following conditions:
1. Save or Die effects, such as Disintegrate.
2. Character HP equal or less than -1 x remaining WP.
3. Character WP equals zero.
4. Ability damage reduces Constitution to zero.
Wound points will be adjusted by any effect that changes Constitution, even temporarily, whether that be a penalty such as Ability damage, or a bonus such as the Endurance spell.
Critical hits inflict HP damage as normal. However, the critical hit also inflicts a number wound points equal to the effective critical multiplier. Thus, a critical hit delivered by a weapon with an effective critical of x3 would inflict 3 WP of damage, in addition to the HP damage. An 18-20/x2 weapon would inflict 2 WP on a successful critical hit. Attacks which inflict subdual damage never cause loss of wound points.
Critical effects may also reduce wound points, as explained below.
CRITICAL EFFECTS
Occasionally, even the hardiest of heroes have to grapple with the effects of grievous wounds. If a character loses more than half of his remaining HP from a single attack, there is a chance that there is a lasting effect from the injury. Creatures which are not subject to critical hits are also immune to these critical effects.
NOTE: These critical effect rules are intended to replace the Massive Damage rule. Instead of forcing a save or die effect, more interesting (and slightly less lethal) conditions may be placed on a severely wounded character.
When a character loses more than half his current hit points from a single attack, spell, or effect (such as falling damage, for example), make a Fortitude save with a DC of 10 + ½ damage dealt. Subdual damage does not count towards this condition, and never causes wounding damage. A successful save indicates no Critical Effect. Failure indicates one of the following Critical Effects, indicated by the unmodified result of the saving throw (the 'natural' roll):
Critical Effect Table (d20)
Limb maimed: roll 1d12 and consult the Damage Location table below. The character is completely unable to use the maimed body part. The character loses 5 wound points due to the maiming. These lost WP may only be recovered with Heal, Regenerate, or an equivalent effect. Sensory organs thus maimed are considered severely damaged. If the character's head is maimed in this fashion, the character is immediately reduced to -1 HP and rendered unconcious.
Stunned: a stunned character cannot act and loses any Dexterity bonus to AC. Attackers get a +2 bonus on attack rolls against a stunned opponent. No loss of wound points occur.
Impairment: reduce WP by the listed number and roll 1d12 for the Damage Location table below. The wounded character suffers a check penalty equal to twice the inflicted WP for any activites associated with the indicated limb or organ, as listed in the DMG under the Damage to Specific Areas variant (p. 66). This check penalty is reduced as WP are recovered by the same 2:1 proportion.
Bleeding wound: a bleeding wound inflicts the indicated number of WP. Additionally, the wound will cause an equal number of HP to be lost each round due to bleeding. Bleeding wound points will not heal naturally (see Healing, below). Once a round, a bleeding character may roll for stabilization (10% on d%) - a successful stabilization roll will stop one point of bleeding, but does not restore lost WP. A successful Heal check with a DC of 15 + current number of bleeding WP will also stabilize one point of bleeding. Stabilized wound points can heal normally.
Ability damage: roll d12 and consult the following table. Apply the listed points of temporary Ability Damage. Note that this effect does not inflict WP, and the ability damage is recovered normally, as according to the PHB (p. 129).
Ability Affected Table (d12)
Clobbered: a clobbered character may only take a partial action on his next turn, but recovers from this condition and the beginning of the next round. No WP are inflicted.
HIT LOCATION
Although hit location is entirely irrelevant to hit point damage, some critical effects are based on damage to a specific body part, generally a limb, head, or sensory organ (Variant: Damage to Specific Areas, DMG, p. 66). Roll d12 and consult the following chart to determine what type of location is affected.
Damage Location Table (d12)
In the case that the affected creature entirely lacks the listed body location type, use the nearest analog limb/organ if there is one, or go up the table to the next highest listing until you achieve an appropriate result.
In the case that the creature has more than one instance of the listed location type, then roll another die to determine exactly which instance is affected. For simple pairs, any die will suffice, where odd indicates left and even indicates right. For more than two instances of the listed location type, roll a die with sides equal to the number of possible locations, or greater as needed. So, for a head shot against a 6-headed hydra, roll d6 for the specific head. If this hydra only had 5 heads for some reason, d6 would still suffice, but would require a re-roll on the result of 6.
HEALING
These house rules de-emphasize the lasting effects of hit point damage while maintaining lasting damage effects through wound points.
Natural Healing: Characters recover hit points at a rate of 1 HP per level per hour of rest. If you undergo complete bed rest, you recover all lost hit points.
Non-bleeding, non-maiming wound points can heal slowly over time with rest only. After each full day of rest, make a Fortitude save with a DC of 15 + current number of wound points lost. If successful, one wound point was naturally healed that day through simple rest. If the injured character is resting under the care of a healer, a Heal check may also be made at the end of the day with the same DC. If successful, a number of wound points equal to the injured character's Fortitude bonus (or a minimum of 1 WP, whichever is higher) are recovered that day. Bleeding wound points must be stabilized before they can heal naturally. Maiming cannot be healed naturally.
Magical Healing: Healing magic that restores lost hit points may also restore lost wound points as well. This happens simultaneously, so a single casting of Cure Light Wounds will heal both the rolled number of hit points and one wound point at the same time. The following table shows the effect of magical healing on wound points, based on the standard divine healing spells. A hit point equivalency column is provided to measure non-standard magical healing effects on the chart. Thus any magical healing effect that can potentially heal 16 (or more) hit points will also heal 2 wound points, for example.
Effects of Healing Magic on Wounds
Note that Cure Minor Wounds does not heal any wound points, but will automatically stabilize one bleeding wound point, if there are any.
Regeneration: Creatures with natural regeneration do not suffer wound point loss from attacks which inflict subdual damage. Attacks which inflict normal hit point damage to the regenerating creature may also inflict wound point damage. Natural regeneration will not affect these wound points.
The spell Regenerate (PHB, p. 244) will heal all maiming and impairing wound points with a single cast, provided that the target is still alive. If no maiming or imparing wound points are present, this spell will still heal a minimum of 1 WP due to its hit point healing feature.
A Ring of Regeneration allows the wearer to heal 1 hit point of damage per level every 5 minutes. Subdual damage is recovered at a rate of 1 hit point per round. If the wearer suffers maiming or impairing wound points, these WP are healed automatically at the beginning the wearer's next turn. Any other wound points inflicted on the wearer are healed by the ring at a rate of 1 WP per hour.
Healing Precedence: Natural healing will restore simple wound points first - those points cause by critical hits or stabilized bleeding wounds. Finally, impairment wound points are healed last by natural processes. Magical healing will restore bleeding wound points first, then restore maiming points if possible, then impairment points, and finally any remaining simple wound points. Regeneration effects will heal all maiming and impairing points first, and if the effect continues, bleeding points next, and remaining simple points last.
I was inspired to write this up based on some of the house rules cooked up by other contributors to this board. So this is not an attempt to be original, so much as to balance out a mixure of existing ideas for spicing up hit point damage. I will probably play test this system in my next game, but I thought I'd post it here just for fun. So, submitted for your (dis)approval...
The following house rules for damage effects are inspired by the VP/WP damage system used in various d20 games (Star Wars, Wheel of Time), and other house rules posted to the ENWorld boards (primarily by Psion and Hong). The Critical Effect rules in particular are almost entirely the work of Psion, and are used here with only small changes. Thanks for the ideas, folks!
WOUND POINTS
In addition to Hit Points, your character also has a number of wound points (WP) equal to his current Constitution score. These wound points are not a substitute for hit points. HP damage is dealt nomally as specified in the Players Handbook. However, instead of the death threshold being -10 HP, under this rule your character does not die until his hit points have been reduced to a negative number equal to your current wound points.
Wound points may be lost through Ability damage to Constitution, critical hits, or critical effects (see below). Loss of wound points will shrink the 'death cushion' of available negative hit points, as specified above. Additionally, if a character is reduced to zero wound points, death occurs immediately, regardless of how many hit points may remain. Wound points are never less than zero.
Thus, under this house rule, character death occurs under the following conditions:
1. Save or Die effects, such as Disintegrate.
2. Character HP equal or less than -1 x remaining WP.
3. Character WP equals zero.
4. Ability damage reduces Constitution to zero.
Wound points will be adjusted by any effect that changes Constitution, even temporarily, whether that be a penalty such as Ability damage, or a bonus such as the Endurance spell.
Critical hits inflict HP damage as normal. However, the critical hit also inflicts a number wound points equal to the effective critical multiplier. Thus, a critical hit delivered by a weapon with an effective critical of x3 would inflict 3 WP of damage, in addition to the HP damage. An 18-20/x2 weapon would inflict 2 WP on a successful critical hit. Attacks which inflict subdual damage never cause loss of wound points.
Critical effects may also reduce wound points, as explained below.
CRITICAL EFFECTS
Occasionally, even the hardiest of heroes have to grapple with the effects of grievous wounds. If a character loses more than half of his remaining HP from a single attack, there is a chance that there is a lasting effect from the injury. Creatures which are not subject to critical hits are also immune to these critical effects.
NOTE: These critical effect rules are intended to replace the Massive Damage rule. Instead of forcing a save or die effect, more interesting (and slightly less lethal) conditions may be placed on a severely wounded character.
When a character loses more than half his current hit points from a single attack, spell, or effect (such as falling damage, for example), make a Fortitude save with a DC of 10 + ½ damage dealt. Subdual damage does not count towards this condition, and never causes wounding damage. A successful save indicates no Critical Effect. Failure indicates one of the following Critical Effects, indicated by the unmodified result of the saving throw (the 'natural' roll):
Critical Effect Table (d20)
Code:
[color=gold]
Roll Effect
---- -------------------------
1 Limb maimed, 5 points
2 Stunned, 4 rounds
3 Impairment, 4 points
4 Bleeding wound, 4 points
5 Ability damage, 4 points
6 Stunned, 3 rounds
7 Impairment, 3 points
8 Bleeding wound, 3 points
9 Ability damage, 3 points
10 Stunned, 2 rounds
11 Impairment, 2 points
12 Bleeding wound, 2 points
13 Ability damage, 2 points
14 Stunned, 1 round
15 Impairment, 1 point
16 Bleeding wound, 1 point
17 Ability damage, 1 point
18 Clobbered
19 Clobbered
20 Clobbered
[/color]Stunned: a stunned character cannot act and loses any Dexterity bonus to AC. Attackers get a +2 bonus on attack rolls against a stunned opponent. No loss of wound points occur.
Impairment: reduce WP by the listed number and roll 1d12 for the Damage Location table below. The wounded character suffers a check penalty equal to twice the inflicted WP for any activites associated with the indicated limb or organ, as listed in the DMG under the Damage to Specific Areas variant (p. 66). This check penalty is reduced as WP are recovered by the same 2:1 proportion.
Bleeding wound: a bleeding wound inflicts the indicated number of WP. Additionally, the wound will cause an equal number of HP to be lost each round due to bleeding. Bleeding wound points will not heal naturally (see Healing, below). Once a round, a bleeding character may roll for stabilization (10% on d%) - a successful stabilization roll will stop one point of bleeding, but does not restore lost WP. A successful Heal check with a DC of 15 + current number of bleeding WP will also stabilize one point of bleeding. Stabilized wound points can heal normally.
Ability damage: roll d12 and consult the following table. Apply the listed points of temporary Ability Damage. Note that this effect does not inflict WP, and the ability damage is recovered normally, as according to the PHB (p. 129).
Ability Affected Table (d12)
Code:
[color=gold]
Roll Ability Score
---- ---------------
1-3 Strength
4-6 Dexterity
7-9 Constitution
10 Intelligence
11 Wisdom
12 Charisma
[/color]HIT LOCATION
Although hit location is entirely irrelevant to hit point damage, some critical effects are based on damage to a specific body part, generally a limb, head, or sensory organ (Variant: Damage to Specific Areas, DMG, p. 66). Roll d12 and consult the following chart to determine what type of location is affected.
Damage Location Table (d12)
Code:
[color=gold]
Roll Location
---- ----------
1 Head
2 Head
3 Eye
4 Ear
5 Leg
6 Leg
7 Leg
8 Arm
9 Arm
10 Arm
11 Hand
12 Hand
[/color]In the case that the creature has more than one instance of the listed location type, then roll another die to determine exactly which instance is affected. For simple pairs, any die will suffice, where odd indicates left and even indicates right. For more than two instances of the listed location type, roll a die with sides equal to the number of possible locations, or greater as needed. So, for a head shot against a 6-headed hydra, roll d6 for the specific head. If this hydra only had 5 heads for some reason, d6 would still suffice, but would require a re-roll on the result of 6.
HEALING
These house rules de-emphasize the lasting effects of hit point damage while maintaining lasting damage effects through wound points.
Natural Healing: Characters recover hit points at a rate of 1 HP per level per hour of rest. If you undergo complete bed rest, you recover all lost hit points.
Non-bleeding, non-maiming wound points can heal slowly over time with rest only. After each full day of rest, make a Fortitude save with a DC of 15 + current number of wound points lost. If successful, one wound point was naturally healed that day through simple rest. If the injured character is resting under the care of a healer, a Heal check may also be made at the end of the day with the same DC. If successful, a number of wound points equal to the injured character's Fortitude bonus (or a minimum of 1 WP, whichever is higher) are recovered that day. Bleeding wound points must be stabilized before they can heal naturally. Maiming cannot be healed naturally.
Magical Healing: Healing magic that restores lost hit points may also restore lost wound points as well. This happens simultaneously, so a single casting of Cure Light Wounds will heal both the rolled number of hit points and one wound point at the same time. The following table shows the effect of magical healing on wound points, based on the standard divine healing spells. A hit point equivalency column is provided to measure non-standard magical healing effects on the chart. Thus any magical healing effect that can potentially heal 16 (or more) hit points will also heal 2 wound points, for example.
Effects of Healing Magic on Wounds
Code:
[color=gold]
Spell Equiv. Effect on Wounds
-------------------- ------ -------------------------
Cure Minor Wounds 1 Stops 1 point of bleeding
Cure Light Wounds 8 Heals 1 wound point
Cure Moderate Wounds 16 Heals 2 wound points
Cure Serious Wounds 24 Heals 4 wound points
Cure Critical Wounds 32 Heals 8 wound points
Heal all Heals all wound points
Regeneration any Special, see below
[/color]Regeneration: Creatures with natural regeneration do not suffer wound point loss from attacks which inflict subdual damage. Attacks which inflict normal hit point damage to the regenerating creature may also inflict wound point damage. Natural regeneration will not affect these wound points.
The spell Regenerate (PHB, p. 244) will heal all maiming and impairing wound points with a single cast, provided that the target is still alive. If no maiming or imparing wound points are present, this spell will still heal a minimum of 1 WP due to its hit point healing feature.
A Ring of Regeneration allows the wearer to heal 1 hit point of damage per level every 5 minutes. Subdual damage is recovered at a rate of 1 hit point per round. If the wearer suffers maiming or impairing wound points, these WP are healed automatically at the beginning the wearer's next turn. Any other wound points inflicted on the wearer are healed by the ring at a rate of 1 WP per hour.
Healing Precedence: Natural healing will restore simple wound points first - those points cause by critical hits or stabilized bleeding wounds. Finally, impairment wound points are healed last by natural processes. Magical healing will restore bleeding wound points first, then restore maiming points if possible, then impairment points, and finally any remaining simple wound points. Regeneration effects will heal all maiming and impairing points first, and if the effect continues, bleeding points next, and remaining simple points last.
