Magic Resistance

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Magic Resistance is an attribute of heroes that reduces Magical damage by a percentage. Heroes can increase their magic resistance with Strength, items, and spells. Heroes innately possess 25% base magic resistance. Visage has 10% base magic resistance instead due to Gravekeeper's Cloak, which can stack extremely high magic resistance passively. Some summons also possess magic resistance.

Formula

Magical damage taken is calculated using the following formula:

actual damage = magical damage × (1 - strength resistance) × (1 - innate resistance) × (1 - first resistance bonus) × (1 - second resistance bonus) × (1 + first resistance malus) × (1 + second resistance malus)

Magic resistance is calculated as follows:

total magic resistance = 1 - ((1 - strength resistance) × (1 - innate resistance) × (1 - first resistance bonus) × (1 - second resistance bonus) × (1 + first resistance malus) × (1 + second resistance malus))

Example: Anti-Mage on level 7 with maxed Counterspell and a Hood of Defiance has a magic resistance of:
1 - ((1 - (23 + 1.3 x 6) × 0.0008) × (1 - 0.25) × (1 - 0.45) × (1 - 0.25))
1 - (0.97536 x 0.75 x 0.55 x 0.75) = 69.8248%

As seen in the formula above, magic resistance is calculated multiplicatively. Magic resistance items may also stack with each other the same way. Because of the way it is calculated, it is impossible to reach 100% magic resistance without it being specifically given by an ability. It also means that 100% magic resistance buffs cannot be reduced.
Magical damage can also be amplified, and is also multiplicative.

Example: Crystal Maiden on level 12 is ethereal and under the effect of Veil of Discord's Magic Weakness:
1 - ((1 - (18 + 2 x 11) × 0.0008) × (1 - 0.25) × (1 + 0.4) × (1 + 0.25)
1 - (0.968 × 0.75 × 1.4 × 1.25) = -27.05%

Magic Resistance Abilities

Hero Abilities
Hero	Ability
Anti-Mage	Counterspell
Oracle	Fate's Edict
Viper	Corrosive Skin

Unit Abilities
Unit	Ability
Spirit Bear	Demolish
Centaur Courser	Cloak Aura
Hellbear

Item Abilities
Item	Ability
Cloak	Passive
Glimmer Cape	Passive
	Glimmer
Hood of Defiance	Passive
Pipe of Insight	Passive
	Insight Aura

Magic Amplification Abilities

This can also be interpreted as Magic Resistance Reduction on the enemy. Regardless, the result is the same.

Hero Abilities
Hero	Ability
Ancient Apparition	Ice Vortex
Elder Titan	Natural Order
Necrophos	Ghost Shroud
Pugna	Decrepify
Skywrath Mage	Ancient Seal

Item Abilities
Item	Ability
Veil of Discord	Magic Weakness
Ghost Scepter	Ghost Form
Ethereal Blade	Ether Blast

Magic Shield

A magic shield absorbs a set amount of magical damage. This mechanic works independently from magic resistance, and the damage absorption occurs before reductions. Does not absorb physical or pure damage. If the unit is spell immune, it will not absorb any damage.

Multiple magic shields do not stack. They are all used up by the same damage instance. This means it is the most effective to use only a single magic shield at a time.

Hero Abilities
Hero	Ability
Ember Spirit	Flame Guard

Item Abilities
Item	Ability
Hood of Defiance	Barrier
Pipe of Insight	Barrier

See also

• Armor
• Damage Amplification
• Damage Types
• Ethereal
• Spell Immunity