Damage Modification Mechanics

1. Damage Types

There are six different damage types in Diablo II: Fire, Cold, Lightning, Poison, Magic, and Physical. Each of these has its own resistance, although only four of them are shown on the character screen.

1.1 Examples of Damage Types

• Fire damage: Firewall (Sorceress) and Fire Arrow (Amazon)
• Cold Damage: Frozen Orb (Sorceress) and Freezing Arrow (Amazon)
• Lightning Damage: Nova (Sorceress) and Lightning Fury (Amazon)
• Poison Damage: Poison Nova (Necromancer)
• Magic Damage: Bone Spirit and Bone Spear (Necromancer) as well as the damage of Berserk (Barbarian)
• Physical Damage: Normal attack and most other non-elemental attacks

1.2 Poison Damage and Poison Length

Unlike other damage types, poison has two values that affect to the total poison damage: poison damage per frame and poison length. The total damage is calculated as poison damage per frame x poison length in frames (there are 25 frames in 1 second). Therefore, there are also two resistance-like abilities that affect poison damage: Poison Resistance and Poison Length Reduction. The former of these affects poison damage per frame and the latter poison length.

2. Damage Modification

There are eight types of damage modification in the game:

• Resistances
• Percentage absorb
• Direct absorb
• Damage reduced by X and Magic damage reduced by X
• Sorceress's Energy Shield
• Necromancer's Bone Armor and Druid's Cyclone Armor
• Unit type modification
• Poison Length Reduction

2.1 Damage Modification Abilities

Damage modification abilities of Diablo II are listed below.

2.2 Magic Damage Reduced by X vs. Continuous (Frame-Based) Attacks

The effect of MDR is reduced against certain continuous attacks. Learn more about it here.

2.3 Unit Type Modification (XvX)

The damage is yet modified by the type of attacker and defender (XvX factor). The different factors are listed in the table below.

2.4  Life gained from absorb

Absorb effects not only reduce damage, but also give you as much life. Absorb gives only so much life as it de facto reduces. The life from absorb is added to one's current life amount, but the sum cannot exceed one's maximum life. Hence, it is possible to take damage even with great amounts of absorb. In fact, if the final damage done exceeds one's maximum life, absorb does not prevent death.

3. Resistance Calculations

3.1 Resistance calculation order and modification effects

Resistances are reduced by certain skills as well as the difficulty penalty. The calculation order for a particular resistance is the following:

1. Resistances

Sum up resistances from all sources (items, skills, etc.) concerning that resistance.

2. Curses and auras that reduce resistances

Subtract the effect of curses and auras that reduce the resistance from the result. If they are cast upon a monster that is immune to the damage type in question, they work at 1/5th effectiveness. These skills are the following:

Skill	Resistances affected	Reduction effect1)
		Normal targets	Immune monster
Amplify Damage (Necromancer curse)	Physical resistance	-100	-20
Conviction (Paladin offensive aura)	Fire, cold, and lightning resistances	-X	-X/5
Decrepify (Necromancer curse)	Physical resistance	-50	-10
Lower resist (Necromancer curse)	Fire, cold, lightning, and poison resistances	-X	-X/5

1) X denotes the reduction value of the skill.

3. Personal resistance reduction skills and properties

Skills and properties, which reduce resistances but are not attached to targets, are calculated next. They do not affect immune monsters, but if the resistance of such monsters is brought below 100 in the previous step, these skills and properties have a full effect.

Skill or property	Resistances affected	Reduction effect1)
		Normal targets	Immune monster2)
Cold Mastery (Sorceress cold skill)	Cold resistance	-X	0
-X% to Enemy Fire/Cold/Lightning/Poison Resistance	Fire, cold, lightning, or poison resistance	-X	0

1) X denotes the reduction value of the skill.
2) Monsters that have a resistance of 100 or more at this step.

4. Difficulty penalty

Apply the difficulty penalty to the result. Difficulty penalty applies only to players and hirelings. It does not affect monsters, golems, and minions.

5. Upper and lower limits

Apply upper and lower limits for the resistance. Note that monsters, golems, and minions have different limits than players and hirelings.

6. Effects that ignore resistances

At this step, skills and item properties that "ignore resistance," such as Sanctuary (paladin offensive aura), take effect. They set the resistance they affect to 0, if it is above 0. A negative resistance is unaffected. This effect applies to only the damage calculation in question, and the game does not modify the actual resistance value of the target.

3.2  Notes on resistance calculations

Skills and item properties that pierce poison resistance also decrease the poison length reduction (PLR). For example, -50% to enemy poison resistance reduces poison resistance and poison length reduction by 50.

The lightning damage of Fists of Heavens does not pierce resistances.

Scroll of resistance, which one receives from Malya in Act V after rescuing Anya, adds 10% to fire, cold, lightning and poison resistances.

4. Application Order

4.1 Damage Modification Effects

There is a well-defined order in which the damage modification effects are applied to the damage:

1. XvX
2. Energy Shield
3. Bone Armor and Cyclone Armor
4. DR and MDR
5. Resistances
6. % Absorb
7. Direct Absorb

In each of these phases, damage cannot be reduced below zero. The result is what I call Damage Taken.

4.2 Special effects

There are some special effects that take place before damage resolution: Thorns, Iron Maiden, Spirit of the Barbs, and Vulpine items (X% Damage Goes To Mana). They all use the physical damage after all damage modification effects, i.e. Physical Damage Taken, as their source damage. For example, Vulpine items add X / 100 x Physical Damage Taken mana to the defender's mana pool in the damage resolution.

4.3 Damage Resolution

Damage and Life Gain

Life gain and damage taken get applied to the target's current life amount in the following order:

1. Add the life gained from absorb effects
2. Reduce life equal to Damage Taken

Mana Damage and Mana Gain

Some effects, such as energy shield and attacks of mana burn bosses, cause you to lose mana instead of life. This is called Mana Damage. Other effects, such as X% Damage Goes To Mana (Vulpine items), cause you to gain mana. These function similarly as life gain and life damage, i.e. the are applied to the target's current mana amount in the following order:

1. Add the mana gained from Vulpine items (and other possible sources)
2. Reduce mana equal to Mana Damage Taken

There are no effects that modify mana damage, and therefore Mana Damage Taken is always equal to Mana Damage dealt by the attacker plus mana damage caused by Energy Shield. Energy Shield causes mana damage equal to (32 - unmodified Telekinesis skill level) / 16 x Damage Absorbed by Energy Shield.

4.4 The Big Picture: Defense, Blocking, and Damage Modification

Defense and blocking are calculated in a to-hit step, which occurs before damage modification mechanics. The exact order of the game mechanics is the following:

1. Check Defense (see to-hit calculations)
2. Check Blocking (shield block is applied at 1/3 when the defender is running)
3. Determine damage done by the attacker, if the attack hits
4. Apply damage modification mechanics

5. Damage Formulas

5.1 Damage Taken and Life Gained

Assuming that damage is not reduced to zero in any step, we get the following equations for damage taken and life gained:

Damage Taken = (Damage * XvX / 100 * (1 - ES / 100) - ArmorSkill - DR) * (1 - Resistance / 100) * (1 - Absorb% / 100) - Absorb

Life Gained = (Damage * XvX / 100 * (1 - ES / 100) - ArmorSkill - DR) * (1 - Resistance / 100) * Absorb% + Absorb

Resistance, Absorb%, XvX, and ES are given as integer values in these equations, such as 50.

5.2 Final Damage

If we further assume that life can be fully added to the character's life amount (it doesn't exceed the maximum), we can calculate the final damage as follows. (It is the damage actually inflicted to the character counting both damage taken and life gained from absorb.)

Final Damage = Damage Taken - Life Gained

By expanding the terms, we get:

Final Damage = (Damage * XvX / 100 * (1 - ES / 100) - ArmorSkill - DR) * (1 - Resistance / 100) * (1 - 2 * Absorb% / 100) - 2 * Absorb

Negative final damage means that you gain life.

5.3 Mana Damage

Furthermore, mana damage taken and mana gained can be represented by the following equations:

Mana Damage Taken = ManaDamage + (32 - TelekinesisBaseLevel) / 16 * Damage * XvX / 100 * ES / 100

Mana Gained = (PhysicalDamage * XvX / 100 * (1 - ES / 100) - BoneArmor - DR) * (1 - PhysicalResistance / 100) * DamageGoesToMana% / 100

Percentage values, such as PhysicalResistance, XvX, and ES, are given as integer values in these equations, such as 50.

5.4 Final Mana Damage

Final mana damage can be calculated the same way as Final Damage, but expanding the terms does not yield a neat formula. Therefore we write that:

Final Mana Damage = Mana Damage Taken - Mana Gained

Negative final mana damage means that you gain mana.

5.5 Terms in Equations

• Damage = Original damage dealt by the attacker
• XvX = Unit Type Modification, see the table above.
• ES = Sorceress's Energy Shield (vs. all damage types except poison)
• ArmorSkill = Necromancer's Bone Armor (vs. physical damage) or Druid's Cyclone Armor (vs. fire, cold and lightning damage)
• DR = Damage reduced by X (vs. physical damage) or Magic damage reduced by X (vs. fire, cold, lightning and magic damage)
• Resistance = Resistance (the appropriate one vs. damage type) or Damage Reduced by X% (vs. physical damage)
• Absorb% = Percentage absorb (the appropriate one vs. damage type)
• Absorb = Direct absorb (the appropriate one vs. damage type)
• TelekinesisBaseLevel = Unmodified level of Telekinesis (sorceress lightning skill)
• ManaDamage = Mana damage dealt by the attacker
• PhysicalDamage = Physical damage dealt by the attacker
• BoneArmor = Necromancer's Bone Armor
• PhysicalResistance = Damage Reduced by X%
• DamageGoesToMana = Damage Goes To Mana %

Acknowledgements

Adamantine for pointing out several omissions and mistakes in an early version of the page updated to the 1.10 version of Diablo 2.
Adeyke for information about resistance calculations.
Assa2 for confirming that magic resistance is not affected by difficulty penalty and that the scroll of resistance does not affect magic resistance.
Caaroid for confirming that Damage Goes To Mana is applied after all damage modification effects.
Jarulf for the application order of the reduction effects and for information about unit type modifications.
Occhidiangela for confirming that magic resistance is not affected by difficulty penalty and that the scroll of resistance does not affect magic resistance.
Ruvanal for testing that MDR applies to fire, cold, lightning and magic damage but not poison damage.
Steve Estes for suggesting to add the application point of Damage Goes To Mana and how defense and blocking relate to damage modification effects.
Valkemen for initially pointing out that magic resistance is not affected by difficulty penalty.