Parry and Armor as DR defense system

Replaces: "Armor class" "Flat-footed Armor Class" "Touch AC" "CMD"

Modifies: "[Worn] Armor" "Natural Armor" "Damage Reduction" "Sneak Attack" "(Improved) Uncanny Dodge" "Feint"

Passive Defense is 10 + all sources of AC except Natural and [Worn] Armor, ie Touch AC plus Shield bonus.

Active defense is Passive Defense + Base attack bonus + Strength bonus - Size penalty. The size penalty is negated in the active defense. A character's active defense cannot be lower than their passive defense.

Characters have a limited number of defense uses per turn. An armed character can Parry one attack per round. A character with a shield bonus (except bucklers) can Block one attack per round. A character under the effects of Haste, a character using the Complete Defense action, or with Improved Uncanny Dodge can either Block, Parry, or Dodge any additional time for each of these effects. A character with Base Attack Bonus +6 or more can make additional active defenses with its iterative attacks. Maneuvers use AD/PD like other attacks. Touch melee attacks and all ranged attacks can be blocked or dodged, but not parried.

Attacks compare their attack rolls to the defender's passive defense score. If the attack is less than the passive defense score, the attack misses. If the defender is aware of the attack, not flat-footed, and has active defense left this round, the attack is also compared to the defender's active defense score. If the attack is less than the active defense score, the attack is Parried, Blocked, or Dodged. The defender chooses the order in which these are expended on their turn. Whether the attack is negated, a use of the active defense is used for the round. If a character's active defense bonus is 0, the character still uses active defense for the purpose of other effects, such as sneak attack.

e.g.: A CR 1/3 orc has 10 PD, 14 ADp, DR 1/adamantine and DC 2/(slashing or adamantine); A CR 7 Dire bear has 10PD, 24/19 ADp, DR 4/A and 8/AoS; a CR 7 invisible stalker has 14PD, 25/20 ADp, DR 3/a, DR 6/AoS; CR 7 falcata fighter 18PD, 26/26/26/26/21AD, DR 2/A, DR 4/AoP

Armor types and properties
 Max Dex
 ACP
 ASF
 Speed

Worn armor grants two levels of damage reduction. The lower is equal to their armor score (see above) plus their enhancement bonus.

Natural armor increases this damage reduction equal to 1/2 of the listed value and enhancement bonus (rounded up). Add listed DR to this.

The first value is overcome only by adamantine. The second value is overcome by either adamantine or a damage type specific to the armor's substance

Bludgeoning: Bone, Chitin, Shell

Piercing: Minerals/stone, Metals, Scales

Slashing: Hide, Textiles, Wood

e.g.: +1 wooden heavy armor grants 4/adamantine and 8/(adamantine or slashing); A CR 19 ancient red dragon has PD 5, ADp 39/34/29/24, 33 natural armor (hide) has 17/adamantine and 34/adamantine or slashing (and DR 15/magic??)

Mithral uses penalties one level lower. Adamantine isn't overcome by adamantine.

Other changes: Sneak attack applies when active defenses cannot be used. Flanking is not sufficient to allow sneak attacks. Uncanny dodge allows active defense to be used while flat-footed or unaware of the attacker.

Combat expertise adds 1 dodge or parry, plus an additional 1 for every 4 BAB. Each additional defense granted applies a -1 attack penalty. A Character with combat expertise can also chose to not use a defense before an attack roll is made against them.

Mage armor grants medium armor with no penalties (2/force, 4/magic or force). Shield grants 2 shield AC and allows the caster to use their (shield spell) caster level instead of base attack bonus.

Feint is a full-round action attack that grants a feint attempt. All attacks are made at a -2 penalty. A successful feint uses up an active defense. Improved feint consumes two defenses. Feint cannot be used with two-weapon fighting unless an exception is made.

Is this actually fun? CMD for NPCs is pretty similar to AC. High NA enemies have ugly amounts of DR, CR 7 earth elemental 11+6 DR, 7PD, 28/23AD (lvl 7 THF fighter 2d6+17)