Magic Resistance

Magic Resistance is an attribute of heroes, extremely similar to Armor. Instead of reducing physical damage, it reduces magical damage. All heroes possess 25% Magic Resistance from their armor type. This percentage is completely independent of their amount of Armor. Certain hero summons, such as Enigma's Eidolons, also possess intrinsic magic resistance.

Damage Reduction/Increase
Normally, all heroes possess 25% Magic Resistance. This means that all magical damage will be reduced 25%, or only take 75% of the nominal spell damage. Any additional effects, such as that from Hood of Defiance will reduce the remaining damage by whatever % Magic Resistance they give. Listing Magic Resistance as a fraction of 1, the total damage taken will be
 * Spell Damage * .75 * (1-Magic Resistance of item)

Likewise, for items that increase magic damage (such as Veil of Discord, the damage take will be
 * Spell Damage * .75 * (1+Magic resistance decrease)

Magic Resistance Stacking
Magic Resistance items do not stack. Therefore, only the last item obtained of Cloak, Hood of Defiance, or Pipe of Insight will grant Magic Resistance.

Stacking Magic Resistance (from items, spells, and naturally) occurs multiplicatively. For an Anti-Mage with Spell Shield, and Hood of Defiance, the total magical damage taken will be .75*.70*.50=.2625 of the nominal damage, or 73.5% Magic Resistance.

Maximum Magic Resistance on Heroes
Heroes without spell resistance skills: No Items: 25% Cloak only: 36.25% Hood only: 47.5%

Spell Shield level 4 gives 50% more spell resistance No Items and skills: 25% Cloak only: 36.25% Hood only: 47.5% Spell Shield only: 62.5% Cloak and Spell Shield stacked: 68.125% Hood and Spell Shield stacked: 73.5%
 * Anti-Mage:

Corrosive Skin level 4 gives 25% more spell resistance No Items and skills: 25% Cloak only: 36.25% Hood only: 47.5% Corrosive Skin only: 43.75% Cloak and Corrosive Skin stacked: 52.1875% Hood and Corrosive Skin stacked: 60.625%
 * Viper:

Flesh Heap level 4 gives 16% more spell resistance No Items and skills: 25% Cloak only: 36.25% Hood only: 47.5% Flesh Heap only: 37% Cloak and Flesh Heap stacked: 46.45% Hood and Flesh Heap stacked: 55.9%
 * Butcher:

Phantom Edge level 3 gives 20% more spell resistance No Items and skills: 25% Cloak only: 36.25% Hood only: 47.5% Phantom Edge only: 40% Cloak and Phantom Edge stacked: 49% Hood and Phantom Edge stacked: 58%
 * Phantom Lancer:

Skills and items that grant Magic Resistance

 * [[Image:Cloak lg.png|Cloak|40px|link=Cloak]] Cloak
 * [[Image:Hood_of_Defiance.png‎|Hood of Defiance|40px]] Hood of Defiance
 * [[Image:Pipe.png‎|Pipe of Insight|40px|link=Pipe of Insight]] Pipe of Insight
 * [[Image:Spell_Shield_icon.png|Spell Shield|40px|link=Anti-Mage#Spell Shield]] Anti-Mage's Spell Shield
 * [[Image:Flesh_Heap_icon.png|Flesh Heap|40px|link=Pudge#Flesh Heap]] Pudge's Flesh Heap
 * [[Image:Corrosive_Skin_icon.png|Corrosive Skin|40px|link=Viper#Corrosive Skin]] Viper's Corrosive Skin
 * [[Image:Phantom_Edge_icon.png|Phantom Edge|40px|link=Phanton Lancer#Phantom Edge]] Phanton Lancer's Phantom Edge
 * [[Image:Gravekeepers_Cloak_icon.png|Gravekeeper's Cloak|40px|link=Visage#Gravekeeper's Cloak]] Visage's Gravekeeper's Cloak

The only the last acquired of the first three will be active at one time.

Skills and items that lower Magic Resistance
Currently, only the Veil of Discord can lower an opponents Magic Resistance. It multiplies all magical damage taken by 25%. Note that this is multiplicative with the hero's existing Magic Resistance, so a hero with only basic Magic Resistance who is affected by the Veil will still take only 94% (or 19% more than they otherwise would) of all incoming magical damage.