Well, it looks like the detailed damage info is going to take awhile so in the meantime here is the combat system that will be the basis for the extended bodily damage. This will give you an idea of where I am heading with the overall tone of combat and the lethality of a Modern Horror campaign. Enjoy!
NOTE 1 : All non-human antagonists ALWAYS make Aimed Shots at specific body parts; the hit location preferred is dependent on the particular monster (check each creature description for specifics).
NOTE 2 : Unlike normal D20 games, the encounters should be vastly over-powered … one and a half to three times the CR of the party in each encounter (why do you think I made the classes so powerful?). But in every case make sure that the Horror has some fatal weakness that is much easier to hit and/or defeat once the heroes know about it (think silver in the Blade movies, a simple scratch will dust a vamp but they are immune to everything else).
5.1 Aimed Shots & Called Shots
One aspect of earlier editions of D&D that is oversimplified in the D20 system is Called Shots, or more accurately, Aimed Shots. The difference is one of perspective – Called Shots are what Protagonists and their NPCs allies perform against Horrors when they are necessary or they just want to show off; whereas Aimed Shots are what Horrors always employ when attacking us lowly Humans. Called Shots are always -4 to the Attack Roll of the Protagonists. Use the following Attack Roll modifiers when Aimed Shots are made against Humans:
-1 / -3 Torso / Skin (when 50% exposed)
-2 / -4 Chest / Abdomen / Whole Back / Whole Leg / Skin (25% exposed)
-3 / -5 Whole Arm / Upper or Lower Leg / Upper or Lower Back / Buttocks / Skin (10% exposed)
-4 / -6 Upper or Lower Arm / Foot / Whole Head / Groin / Left or Right Buttock
-5 / -7 Neck / Whole Hand / Ankle / Knee / Hip / Shoulder / Face / Skin (1% exposed)
-6 / -8 All Fingers / All Toes / Mouth / Heart or Breastbone
-7 / -9 Individual Fingers or Toes / Eye / Ear / Nose
-8 / -10 Any body part smaller than a finger or eye.
The first modifier is always used for NPCs and Victim Protagonists, the 2nd modifier is used for all other Player Protagonists. This modifier is halved if the attack is a full round action (any damage taken incurs a Concentration check otherwise the standard modifiers apply).
5.2 Hit Points
Hit points don’t work exactly the same as in other D20 rules systems. Consider Hit Points to be raw durability when viewed overall and actual physical durability only on a body part by body part basis. For Aimed Shot purposes consider each body part to have hit points based on the following formulae:
Tiny Body Parts (-6 / -8 modifier and lower) CON + DEX modifiers only (minimum to start is 1 LHP in each Tiny Body Part Location)
Small Body Parts (-4 / -6 modifier to -5 / -7 modifiers) 1 hit point per character level + DEX modifier.
Medium Body Parts (-2 / -4 to -3 / -5 modifiers) 2 hit points per character level + CON modifier.
Large Body Parts (-1 / -3 modifier only) 3 hit points per character level + CON and STR modifiers.
NOTE 1 : Any damage taken to Location Hit Points (LHP) is also applied to overall HP. For example, if a Protagonist takes 3 LHP to his left arm that also removes 3 points from his overall HP. This means a low-level character can be knocked out without taking very much location damage.
NOTE 2 : Double Max : whenever a Protagonist takes double the maximum LHP from a single attack to an individual body part then that body part is considered to be removed or destroyed (with the attendant screaming and profuse bleeding leading to a probable death unless immediate emergency medical care is applied). Refer to the corresponding body part in Section 5.6 for more details.
NOTE 3 : Critical Hits: If a critical hit occurs during an attack to a body part then the DM is to refer to the results under section 5.6 after a successful 2nd roll (the called shot negative modifier applies to the 2nd roll of course). These results supersede normal critical hit rules.
NOTE 4 : Any damage that does not reduce a body location to 0 HP can be healed to full location HP with a successful Treat Injury DC (20 + HP to be healed) check with a First Aid kit. Important : this does not heal your normal HP just the HP for that location (thus, if you took 3 damage to your leg that brought you down from 30 to 27 hit points and had field surgery on it you would still be at 27HP even though your leg would be back to full health). This requires 5 minutes of uninterrupted attendance by the Surgeon to work. A skill check fail still heals 1 HP to that location.
Body part damage is excruciatingly painful compared to standard D20 damage, after all you may have been sliced open and bleeding or gods forbid you lost a body part. Any damage that drops a body part to 0 location HP causes a Pain Level to the Protagonist. Each Pain Level incurs a -1 to attack rolls, damage rolls, skill checks and all saving throws, as well as a 5‘ combat movement penalty. NOTE: Each feat placed in Toughness abates 1 Pain Level.
5.4 Physical Rehab
After especially violent encounters a Protagonist may be missing one or more body parts. With time, patience and sweat the Protagonist can recover some or (remotely) all of his former functionality. The after effects of catastrophic injury are very time sensitive to rehab, all rehab programs must be undertaken within 1 month of receiving initial treatment for the injury.
Standard physical rehab can be undertaken for free with proper supervision, this means that STR CON and DEX are easily regained. Scarring and brain damage are an entirely different matter. CHA costs $10,000 per point to repair. INT, WIS and neurological DEX damage costs $1,000 per point to repair.
In all cases it takes 1 month per point of stat damage for rehab. Thus, if the Protagonist has had a particularly violent encounter and suffered 2 pts of STR damage and 1 pt of CHA damage it would take 3 months and $10,000 for complete rehab.
5.5 Treat Injury Skill
Treat Injury gains more capabilities under these combat rules. Pain Relief allows the practitioner to remove one Pain Level that has been inflicted within the last 5 minutes. It requires bandages, splints, thread, needles and a basic pain reliever (aspirin or Tylenol). It takes a full minute to perform and is DC 15.
Staunch Wound allows the practitioner to stop a single bleeding wound (each application of bleeding is cumulative in effect but each application is to be considered a separate wound for purposes of skill use). It requires bandages, gauze, rubbing alcohol, thread and needle. One wound can be closed per full round usage of this skill and a DC 15 check.
Triage Surgery allows the medic to reduce the severe after-effects of Critical Injuries. If immediately applied within 5 combat rounds of the critical hit and a DC 20 check is successful then all stat loss from the wound is reduced by a single point (thus a head wound that causes 2 CHA and 3 INT loss will be reduced to 1 and 2 points respectively). This takes a full combat round and a complete medical kit (a First Aid kit just won’t cut it).
Preserve Limb may be employed when the inevitable happens and a Protagonist suffers a forced amputation. A DC 20 check is made and if successful the limb will be preserved for a number of minutes equal to the base rank of the medic (if he spent 4 earned skill points on Treat Injury then he can preserve a limb for 4 minutes). This can be increased to hours rather than minutes if the medic has access to a cooler and a large supply of ice (thus 4 hours instead of 4 minutes in the above example). The only place a limb can be reattached is a fully equipped hospital.