Armor as Damage Reduction
While the armor and Armor Class system presented in the Pathfinder Roleplaying Game is tried and tested, some players may yet have a sense that it feels slightly off. That is to say, if a suit of armor is actually protecting the wearer from attacks that strike but simply fail to cause the wearer harm, why then do we say that armor reduces the chance of a hit? The abstraction has been clarified in the rules by defining what it means to be “hit” in combat as actually being “hit in such a way as to effectively cause harm,” but this explanation is still not enough for some players.
The following is an alternative system that allows armor to absorb the damage of attacks, rather than a system that provides an abstract way of determining when a hit does actual harm. Like all the rules presented in this chapter, it is a variant to the base system of the Pathfinder RPG. It is for GMs who want armor to reduce damage rather than increase Armor Class, and replaces the normal rules for armor.
In this system, a creatures no longer has an Armor Class. Instead it has a Defense score that a foe's attack roll must meet or exceed to hit the creature. Then any damage is reduced by damage reduction based on the creature's armor worn and any natural armor bonus the creature has. Furthermore, armor has a chance of reducing all critical hits to normal hits, by replacing the confirmation roll for critical hits with a critical defense check made by the creature threatened by the critical hit.
Defense
In this alternative system, a creature does not have an Armor Class (AC); it instead has a Defense score.
Defense = 10 +Class Bonus + shield bonus + Dexterity modifier + other modifiers
Touch Defense = 10 + 1/2 Class Bonus(Rounded Down) + Size, Dexterity Modifier, Deflection modier.
Defense represents how easy or difficult it is to hit a creature. The shield bonus is added because a creature is considered to be actively blocking attacks with its shield whenever it can, which is whenever it would gain its Dexterity bonus to AC and not be flat-footed.
Losing Dexterity Bonus to Defense: Situations or effects that would cause you to lose your Dexterity bonus to AC instead cause you to lose your Dexterity bonus to Defense. Also, whenever you lose your Dexterity bonus to Defense, you also lose any shield bonus to Defense, since when you lose your Dexterity bonus to AC, you also lose the ability to properly respond to attacks with your shield.
Flat-Footed Defense: You do not gain your Dexterity or shield bonus to your Defense if you are flat-footed or lose your Dexterity bonus to Defense; thus, your Flat-Footed Defense is equal to your Defense minus your Dexterity bonus and shield bonus.
Defense and Using a Shield without Proficiency: When a creature uses a shield it is not proficient with, it takes that shield's armor check penalty as a penalty to the shield bonus, along with the other penalties for using a shield without proficiency. Furthermore, it also takes this penalty to its Flat-Footed Defense, as the shield actually gets in the way instead of defending against incoming attacks.
Armor as Damage Reduction
Armor in this system keeps all of its normal statistics and qualities, but its armor bonus (including any enhancement bonus added to armor bonus and natural armor bonus) is converted to DR/armor. The DR an armor provides is equal to its total armor bonus provided that the creature wearing the armor is also proficient with the armor.
Using Armor without Proficiency: Creatures using armor they are not proficient with only gain half DR from it on top of any of the other normal penalties for using armor without proficiency.
DR/Armor: This type of DR blocks the damage of all attacks that would normally be affected by DR, based on the composition of the armor (see Table 5–1). Unlike most forms of damage reduction, DR/armor stacks with other types of DR. For instances, when fighting a skeleton with DR 5/bludgeoning and DR 4/armor (+2 for armor, +2 for natural armor), the skeleton's DR/armor reduces 9 points of damage from non-bludgeoning attacks, and 4 damage from bludgeoning weapon attacks. Magic weapons and attacks from Huge or larger creatures bypass the DR 4/armor, but not the DR 5/bludgeoning.
Natural Armor Bonus and DR: Like a creature's armor bonus, a natural armor bonus is also converted into damage reduction. If a creature is wearing armor and has a natural armor bonus, the creature adds its armor bonus to its natural armor bonus to determine the amount of DR/armor that it has (see Table 5–2).
For instance, if a creature wearing a +2 chain shirt has DR 6/armor is then subject to a barkskin spell cast by a 6th-level druid (gaining a +3 natural armor bonus), its DR becomes DR 9/armor for the duration of the spell. This DR is bypassed by adamantine, or the attacks of Gargantuan or larger creatures.
A creature that has both DR from a source other than armor and a natural armor bonus gains the effects of an enhanced form of DR, similar to how the composition of the armor grants special DR/armor defenses (see Table 5–1). If a creature has magical armor, natural armor, and DR, it takes the best form of the special protection provided by both its armor and its mix of DR and natural armor to its DR/armor.
For instance, if a creature has natural armor and DR/magic and is wearing adamantine armor, that creature's DR/armor functions as DR/—, and can be bypassed by Colossal or larger creatures, since the adamantine armor provides the best of the two damage reductions.
Unusual Creatures and Armor DR: Amorphous or incorporeal creatures have an easier time bypassing DR/armor. When they attack a creature with DR/armor, they typically treat that DR as a fraction of the DR/armor. Attacks by incorporeal creatures entirely ignore the DR unless that DR comes from a force effect or from armor with the ghost touch special armor quality. These traits are detailed in Table 5–3.