I'd like to redo the wiki page on damage reduction, but it's much easier to deal with multiple edits/previews here on the forums. So the work-in-progress will be done here in this thread.
Damage Reduction (DR) is a measure of how much weapon damage a character can ignore before losing hit points. The DR value is subtracted from each incoming hit, to a minimum of zero damage received. If you have a DR 10 and get hit for 9 points of damage, you take no damage at all. If you have a DR 10 and get hit for 15 points of damage, you only take 5 points of damage. DR applies only to physical weapon damage, although there is a similar concept of Resist Energy that applies to energy/elemental damage from spells, enchanted weapons elemental damage, and non-physical traps.
Damage Reduction is applied before the reduction from your Physical Resistance Rating.
Active vs Passive
Passive DR is shown on your character sheet in the area below your ability scores. Multiple DR entries may be listed on your sheet, but only the highest applicable passive DR applies. The actual DR used against an attack is reported in the combat log as final/net damage dealt followed by damage reduced.
Active DR applies when a you actively block by holding down the shift key. Active DR is displayed as "Blocking DR" in the expandable area of your inventory sheet. (Click the "Details" button on the bottom right to open it.) Active DR cannot be bypassed except by melee attacks from behind; benefits of blocking apply only to melee attacks against the character's front 180°. Furthermore, Active DR stacks with Passive DR. (Active DR stacks with only the highest passive DR that applies.)
Passive DR - Sources
- Barbarians get +1 DR/- at levels 2, 5, 8, 11, 14, 17, 20 and a +1 Enhancement available at levels 3 and 7
- Favored Souls are granted DR10/X at level 20, where X is a type of damage based on their Faith enhancements that are chosen at level 1
- Monks gain DR10/Epic at level 20 via the granted feat Perfect Self
- Warforged Adamantine Body, Improved DR Feats, or Warforged Improved DR enhancements (DR/Adamantine)
- Stacking Half-Elf Improved Damage Reduction with the Barbarian Dilettante Feat (DR 1/- or 2/-).
- Stoneskin spell (DR 10/Adamantine)
- Angelskin spell (DR5/Evil)
- Ironskin Chant (DR5/-) song from Warchanter Bard
- House Deneith Defender airship buff (DR 1/-)
- Adamantine Armor DR/- (1 from shields or light armor, 2 from medium armor, and 3 from heavy armor)
- Item effects (Invulnerability, Axeblock, Hammerblock, Spearblock, Bracing, Bolstering, Buttressing, etc...)
- Named items (see Passive DR - Types below)
The Warforged Feats and Enhancements that improve DR are special cases. These benefits explicitly say they grant DR/Adamantine or improve your existing DR/Adamantine. They stack with your single strongest other source of Adamantine DR, whether it comes from a Warforged racial benefit or something else.
Passive DR - Types
For an example, consider a cleric wearing Epic Cavalry Plate (DR/Chaotic) and Ghost-Waking Cloak (DR/Evil) using Light and Darkness (DR/Epic) for a shield. If running Epic Zawabi's Revenge, Queen Lailat will bypass all of this DR by virtue of being a Chaotic Evil Outsider epic raid boss. If we switched from Light and Darkness to a Wall of Wood (DR/Slashing), Lailat would still fully bypass because her khopeshes deal slashing damage.
- DR/- (items) cannot be bypassed by anything. For example, this is the kind of DR that elementals have. This effect can be simulated by wearing a combination of axeblock, spearblock and hammerblock items.
- DR/Adamantine (items)
- DR/Bludgeoning (items) can be simulated by equipping both an Axeblock and Spearblock item. This is a common DR profile for new players, equipping Spearbane and Furor's Hide. Monsters that deal bludgeoning damage include Trolls, Bugbears?, ...?
- DR/Piercing (items): Monsters that deal piercing damage include Sahuagin, Kobolds, Spiders, ...?
- DR/Slashing (items): Monsters that deal slashing damage include Orcs, Hobgoblins, ...?
- Axeblock (items) only blocks slashing damage. Technically it is DR/Bludgeon or Piercing.
- Hammerblock (items) only blocks bludgeoning damage. Technically it is DR/Slashing or Piercing.
- Spearblock (items) only blocks piercing damage. Technically it is DR/Slashing or Bludgeon. This is a particularly useful DR for brand new players, as most of the enemies in Korthos as well as low level harbor quests do piercing damage.
- Invulnerability (items) is DR/Magic, which can only be bypassed by weapons with an enhancement bonus. As a general rule, mobs start using magical weapons in the 8-12 level range. That makes the Invulnerability item effect start to lose its luster around level 10. Invulnerability is easy to craft and the effect alone leaves an item ML1, making Invulnerability the preferred armor effect for experienced players during low levels.
- DR/Good (items) can only be bypassed by Good Outsiders. The only Good Outsider enemies in the game are Eladrin in the quest Running with the Devils, and they almost never melee attack anyway, preferring to spam Ray of Light attacks which are spell-like abilities that aren't subject to DR. This makes DR/Good functionally equivalent to DR/-.
- DR/Evil (items) can only be bypassed by Evil Outsiders. All evil outsiders will bypass DR/Evil EXCEPT Bezekira, Hags, Jariliths, Rakshasas, Tieflings, ...? Monsters shooting evil arrows will NOT bypass DR/Evil.
- DR/Lawful (items) can only be bypassed by Lawful Outsiders. (unconfirmed)
- DR/Chaotic (items) can only be bypassed by Chaotic Outsiders. (unconfirmed)
- DR/Epic (items) can only be bypassed by epic raid bosses. These include Velah, Lailat, Xy'zzy and Spawn of Xy'zzy.
Damage Reduction Scaling
Damage Reduction Scaling works similarly to Dungeon Scaling, except it applies to damage reduction, and applies to both players and monsters. Note unlike Dungeon Scaling this only happens in Casual, Normal and Hard Dungeons. Not elite/raid/epic (Dungeon scaling does apply on elite).
Player versus monster
This scaling helps players who otherwise can't bypass or overcome a monsters damage reduction at all, still deal some damage. For any physical attack that would otherwise be completely negated, this scaling allows them to deal 50%/25% of the damage they would have otherwise dealt if the enemy had no damage reduction.
- Normal: DR scaling fully applies - you deal 50% of the damage if your attack would of otherwise been negated.
- Hard: DR scaling applies, but at half strength - you only deal 25% of the damage.
- Elite/Epic/Any Raid: DR Scaling is disabled. Attacks may be reduced to zero.
Examples (Normal difficulty):
- Player swings his +4 Greatsword at a Ghostly Skeleton which has DR100/Good. He would have dealt 40 damage, with all 40 points being stopped by the DR. However due to DR scaling, he instead deals 20 damage to the skeleton.
- Player swings his +4 Greatsword at a Ghostly Skeleton which has DR100/Good. This time he would have dealt 135 damage. Since this is above the damage reduction of the enemy, scaling does not need to happen, thus he deals 35 damage.
Monsters versus player
If a player has some form of damage reduction a monster can't bypass, it's only applied without scaling being taking into account, if that amount would result in less damage then just the scaling. This means that damage reduction can seem far less effective when solo in scalable dungeons, as enemy damage is heavily scaled down, but this only happens after damage reduction.
- Monsters attack is calculated out to deal 20 damage, if no dungeon scaling was in effect at all. Player has DR10/Silver and the monster doesn't bypass this. The player is in the dungeon solo, as such the monster only deals 20% of his regular damage, thus 4 damage. The calculation is applied like this:
- A) 20 damage dealt dungeon scaling scales that damage down to 4 points.
- B) Damage reduction is calculated ignoring scaling. 20 damage, 10 was stopped. 10 damage is dealt.
- C) The lowest of the 2 damage values is applied. This is displayed in a masked way to fool the player: Enemy hit you for 4 damage, 10 was stopped.
Essentially damage reduction does nothing for the player in this scenario due to how it is coded.