Magic Resistance

Magic resistance is an attribute of heroes, similar to armor. Instead of reducing physical damage, it reduces magical damage. All heroes, except Meepo and Visage, 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.

Magical Damage
Magical damage is a special damage type caused mostly by abilities. Unlike physical damage, it isn't reduced by armor. However, it is reduced by magic resistance, and will not affect targets that are magic immune or buildings that are fortified. Ethereal units will also take 40% amplified magical damage.

Mixed damage is similar to magical damage. It is reduced by magic resistance and armor, but ignores magic immunity. Mixed damage does not affect ethereal units.

Damage Reduction
All Heroes have a natural 25% magic resistance, except for Meepo and his clones, who have 35% and Visage, who has 10%. This means that, by default, for most heroes, all magical damage is reduced by 25%, or only 75% of the ability's damage. Any additional effects, such as the bonus given by Hood of Defiance, will reduce the remaining damage by their resistance.


 * Actual damage = magical damage × (1 + magic amplification) × (1 + second souce of magic amplification ) × (1 − natural resistance) × (1 − magic resistance of item) × (1 − magic resistance of first ability) × (1 − magic resistance of second ability)

In the formula above, natural resistance is 0.25 for all heroes except 0.35 for Meepo and 0.1 for Visage.

Magic resistance items do not stack. Only the most powerful magic resistance effect in a Hero's inventory will provide a bonus. Stacking magic resistance of different types (natural, from item, from ability) occurs multiplicatively. For example, an Anti-Mage with Spell Shield, and Hood of Defiance will have 73.75% magic resistance (in other words will only receive 26.25% of any magical damage).

Sources of Magic Resistance

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Magic Resistance Reduction
Magical damage can also be amplified through reduced magic resistance, it also stacks multiplicatively. For example, if a target is both Decrepified and under the effect of a Veil of Discord, the total damage the inflicted hero(with normal base magic resistance of 25%) will take is 140.625% (0.75*1.5*1.25). The only exception is Ghost scepter/Ethereal blade with Decrepify. Under the effect of both Ghost scepter/Ethereal blade and Decrepify, only the amplification with higher value counts. (Effect of Ghost scepter and Ethereal blade is consider alike because they are in the same item-tree)

Sources of Magic Amplification

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Anti-magic Shell
Unlike passive magic resistance, Anti-magic Shell effects absorb a set amount of magical damage and then expires. While the Shell is active, affected units will not take any magical or universal damage, though they can still be affected by a spell's secondary effects such as a stun or slow. Other damage types will bypass the Shell and will reduce its remaining health.

The amount of damage the Shell takes is calculated before magic resistance. Instances of damage exceeding the Shell's remaining health will be reduced by that amount and the remainder will deal damage to the target unit. For example, if a Level 4 Dagon is cast on a unit with a 400 HP Anti-magic Shell, the unit will take 300 magic damage, since it delivers 700 magic damage. Only that 300 damage is further reduced by Magic Resistance, to 225 damage factoring base resistance.

Sources of Anti-magic Shell

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