Damage and stacking
Three different things reduce a hit, and they are applied in this order:
- Damage immunity, a percentage, taken off the total.
- Damage resistance, a flat amount, taken off each type separately.
- Damage reduction, a flat amount, taken off physical damage.
A creature with 50% fire immunity and fire resistance 20 hit for 100 fire takes 50 after the immunity, then 30 after the resistance.
Damage immunity
A percentage of a damage type that is subtracted - or added, when it is a vulnerability. Percentages of the same type add together, from items, spells, feats and race alike, and the total is capped at 100%. A vulnerability of the same type cancels an immunity point for point.
While the net is above zero, at least one point is always absorbed, so 90% immunity against a 10-point hit leaves 1 point of damage rather than 1.
Damage resistance
A flat amount of one damage type, ignored on every hit - "fire 20" absorbs the first 20 fire damage each time. No weapon can punch through it.
Resistances do not stack: for each type, only the highest from a spell or an equipped item counts. The exception is the energy resistance feats, which stack with the rest and are applied before it.
A weapon's elemental damage is resisted per component, so one hit can meet several of your resistances at once. A weapon dealing two physical types is resisted at the lower of the two.
Damage reduction
Also called soak. It is written 20/+3: it ignores the first 20 points of physical damage from any weapon whose enhancement is below +3. Feats and class abilities give it as 20/-, which nothing gets through.
- Reductions do not stack. The one that soaks the most, among those the attacker's weapon does not beat, is the one that applies; on a tie the oldest one wins.
- The exceptions: the epic damage reduction feats stack with Perfect Self, and the X/- sources - barbarian, dwarven defender and the epic feats - stack with each other.
- A creature attacking with its own natural weapons pierces reduction up to its own: a creature with 10/+5 is not stopped by anything up to X/+5. Its X/- reduction does not help with that.
What stacks, and how far
| Stacks | Ceiling | |
|---|---|---|
| Ability score bonuses | yes | +12 |
| Attack bonuses | yes | +20 |
| Damage bonuses | yes | +100 |
| Saving throw bonuses | yes | +20 |
| Skill bonuses | yes | +50 |
| Damage immunity and vulnerability | yes | 100% either way |
| Armour class of different types (armour, shield, deflection, natural, dodge) | yes | - |
| Dodge armour class | yes | +20 |
| Armour class of the same type, dodge aside | no | - |
| Concealment | no | - |
| Damage reduction | no, except the sources named above | - |
| Damage resistance | no, except the energy feats | - |
| Spell resistance | no | - |
Penalties are gathered the same way and kept separate: where something does not stack, the largest bonus and the largest penalty both apply. The ceiling is applied after the two are added, so a character at +24 dodge who takes a -2 dodge penalty is still at +20.
A single item cannot carry more than +12 of saving throw bonus, whatever the character's ceiling is.