Magic resistance
Magic resistance is an attribute that reduces magical damage the unit receives. It acts as a counter part to armor, which grants physical damage resistance. All heroes have magic resistance, while most non-hero units have none. On heroes, similarly to armor, magic resistance scales with levels, increasing by 0.08% with each point of strength the hero has. Strength heroes gain 25% more than agility and intelligence heroes, gaining 0.1% per strength. There are many abilities and items which can boost or reduce a unit's magical armor.
Contents
Magical damage[edit]
Magical damage is a type of damage caused mostly by abilities. Unlike physical damage, it is not affected by armor. However, it is affected by magic resistance dealing more or less damage, depending on the unit's current magic resistance. Besides magic resistance, magical damage, just like physical and pure damage, is also affected by damage manipulation.
Mechanics[edit]
Magic resistance affects magical damage exclusively. It does not matter whether it is spell damage or attack damage, as long as it is magical, it is reduced. Even if magical damage has the HP Removal flag, it is still affected by magic resistance and reduced accordingly.
Stacking[edit]
All sources of magic resistance stack diminishingly. This means a unit's status resistance value changes less, the higher its status resistance is, and more, the lower it is. However, this does not mean a reduction in effectiveness with multiple sources. See the next section for details.
The magic resistance gained through strength is all summed up into, and treated as one instance, which stacks diminishingly with other sourcers. This means with a theoretical strength of 1250, a hero would have 100% magic resistance.
Formula
For total magic resistance of a unit (multiply the result by 100 to get the percentage value):
- Total magic resistance = 1 − ((1 − natural resistance) × (1 - strength × %) × (1 − first resistance bonus) × (1 − second resistance bonus) × (1 + first resistance reduction) × (1 + second resistance reduction))
For magical damage after magic resistance:
- Actual damage = magical damage × (1 − natural resistance) × (1 - strength × %) × (1 − first resistance bonus) × (1 − second resistance bonus) × (1 + first resistance reduction) × (1 + second resistance reduction)
Example:
- Anti-Mage with level 4 Spell Shield and a Cloak has a magic resistance of:
- 1 - (1 - 0.25) × (1 - 0.5) × (1 - 0.15) = 68.125%
- Visage on level 25 under the effect of Veil of Discord and a level 4 Decrepify cast by an enemy has a magic resistance of:
- 1 - (1 - 0.1) × (1 - (96 × 0.08)) × (1 + 0.25) × (1 + 0.6) = -66.176%
With a theoretical strength of 1250 (1000 for strength heroes), magic damage is fully negated. There are several abilities which grant 100% magic resistance. Because of the stacking rules, these abilities prevent a unit's magic resistance to be reduced or increased, as the formula will always result in 100%, no matter how big the magic resistance bonus or reduction.
Effective HP[edit]
Despite each source of magic resistance increasing the magic resistance value less the higher it is and making them seem less effective, each sources increases the unit's effective HP against magical damage by their base value. Effective HP means, how much damage can a unit take before dying, after reductions. In this case, magic resistance increases a unit's effective HP against magical damage. A unit with 0% magic resistance has 100% effective HP against magical damage, means magical damage equaling 100% of its health is required to kill it. Most heroes have 0.25 magic resistance by default, making their effective HP against magical damage 133.33%.
Formula:
- Effective HP = Total HP / (1 - magic resistance)
Instead of 'diminishing' in effectiveness, multiple sources of resistance are actually more effective stacked than they are individually. Two sources of 25% resistance stacked provides 78% extra EHP whereas one source provides 33%.
Example:
- Anti-Mage has 1172 health at max level. With his basic magic resistance, max level Spell Shield and a Cloak, he has an effective HP of:
- 1172 / (1 - 68.125 × 0.01) = 3676.86 effective HP
- Visage has 1928 health at max level. With his basic magic resistance, while under the effect of Veil of Discord and an enemy level 4 Decrepify, he has an effective HP of:
- 1928 / (1 - -80 × 0.01) = 1071.11 effective HP
Magic resistance on units[edit]
| Unit | Base magic resistance | Cloak Aura |  (Aura)
|
 
|
|
(Item + Aura)
|
(Ability)
|
|---|---|---|---|---|---|---|---|
| Standard hero | 25% | 32.5% | 32.5% | 36.25% | 43.75% | 52.75% | 64.94% / 58.75% |
| Visage | 10% | 19% | 19% | 23.5% | 32.5% | 43.3% | 57.93% / 50.5% |
| Pudge (level 4 Flesh Heap) | 35.5% | 41.95% | 41.95% | 45.18% | 51.63% | 59.37% | 69.85% / 64.53% |
| Rubick (level 4 Null Field) | 41.5% | 47.35% | 47.35% | 50.28% | 56.13% | 63.15% | 72.65% / 67.83% |
| Viper (level 4 Corrosive Skin) | 43.75% | 49.38% | 49.38% | 52.19% | 57.81% | 64.56% | 73.7% / 69.06% |
| Anti-Mage (level 4 Spell Shield) | 62.5% | 66.25% | 66.25% | 68.13% | 71.88% | 76.38% | 82.47% / 79.38% |
| Huskar (level 4 Berserker's Blood) | 62.5% | 66.25% | 66.25% | 68.13% | 71.88% | 76.38% | 82.47% / 79.38% |
| Spirit Bear (level 4) | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% / Expression error: Missing operand for -.% |
| Warlock's Golem | Expression error: Unexpected * operator.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | - | - | - | Expression error: Missing operand for -.% |
| Familiars | Expression error: Unexpected * operator.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | - | - | - | Expression error: Missing operand for -.% |
| Necronomicon summons | Expression error: Unexpected * operator.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | - | - | - | - |
| Spiderlings, Spiderites, Eidolons, Mud Golems & Shard Golems | Expression error: Unexpected * operator.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | - | - | - | - |
| Roshan | Expression error: Unexpected * operator.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | - | - | - | - |
| Ancient creeps | Expression error: Unexpected * operator.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | - | - | - | - |
| Siege creeps & Lycan Wolves | Expression error: Unexpected * operator.% | Expression error: Missing operand for -.% | Expression error: Missing operand for -.% | - | - | - | - |
Sources of magic resistance bonus[edit]
Magic Resistance Bonus: 20%/30%/40%/50% (
45%/55%/65%/75%)
Passive.
Radius: 900
Hero Magic Resistance Bonus: 10%
Non-Hero Magic Resistance Bonus: 20%
Multiple sources of Cloak Aura stack.
Magic Resistance Bonus: 15%
Passive.
Magic Resistance Bonus: 15%
Passive.- Magic Resistance Bonus: 45%
Duration: 5
Glimmer provides the magic resistance bonus only while invisible. Has a 0.6 seconds fade time and reapplies itself for the duration. 
Magic Resistance Bonus: 25%
Passive.
Max Magic Resistance Bonus: 20%/30%/40%/50%
Passive. Grants magic resistance for each point of health missing, reaching the cap at 10% health.
Magic Resistance Bonus: 30%
Passive.- Radius: 900
Magic Resistance Bonus: 10% 
Magic Resistance Bonus: 6%/8%/10%/12%
Passive.
Radius: 1200
Magic Resistance Bonus: 10%/14%/18%/22% ( 15%/19%/23%/27%)
Aura. When toggled to defensive mode.
Magic Resistance Bonus: 33%
Passive. Only available on level 4.
Magic Resistance Bonus: 10%/15%/20%/25%
Passive.
Sources of magic resistance reduction[edit]
Radius: 275
Magic Resistance Reduction: 15%/20%/25%/30% ( 23%/28%/33%/38%)
Vortex Duration: 16
The effect lingers for 0.5 seconds.
Radius: 350
Base Magic Resistance Reduction: 40%/60%/80%/100%
Only reduces base magic resistance, ignoring magic resistance bonuses. The aura's debuff lingers for 1 second.
Magic Resistance Reduction: 40%
Enemy Duration: 3
Ally Duration: 4
Does not stack with the reductions of other ethereal effects, the one with higher value takes priority.
Magic Resistance Reduction: 40%
Duration: 4
Does not stack with the reductions of other ethereal effects, the one with higher value takes priority.
Magic Resistance Reduction: 30%
Duration: 3/3.5/4/4.5
Does not stack with the reductions of other ethereal effects, the one with higher value takes priority.
Enemy Magic Resistance Reduction: 30%/40%/50%/60%
Ally Magic Resistance Reduction: 25%
Duration: 3.5
Does not stack with the reductions of other ethereal effects, the one with higher value takes priority.- Radius: 1200
Enemy Magic Resistance Reduction: 10%/14%/18%/22% ( 15%/19%/23%/27%)
When toggled to offensive mode. The aura's debuff lingers for 0.5 seconds. 
Magic Resistance Reduction: 30%/35%/40%/45% ( 45%/50%/55%/60%)
Duration: 3/4/5/6
Radius: 600
Magic Resistance Reduction: 25%
Duration: 16
Radius: 300
Enemy Magic Resistance Reduction: 10%/15%/20%/25%
Duration: 8
The effect lingers for 0.5 seconds.
Sources of 100% magic resistance[edit]
These abilities grant 100% magic resistance to the affected units, reducing every magical damage they take to 0, and ceasing the effects of magic resistance reductions.
Duration: 10/9/8/7/6/5
Duration decreases with each use, capped at 5.
Duration: Permanent
Duration: Whole leap duration or up to 5 seconds, whichever is shorter.
Duration: 5 ( 6)
Duration: 0.8/2/3.2 (
2/3.2/4.4)
Provides immunity until Omnislash stops. Does not dispel any buffs and debuffs.
Duration: 3/4/5/6 ( 5/6/7/8)
Duration: 0 ( 5)
Duration: 0 ( 1 + 0.3 per bounce)
The affected unit's HUD does not reflect the bonus granted by Stone Gaze (when upgraded Mystic Snake applies the same modifier as Stone Gaze).
Duration: 3
The affected unit's HUD does not reflect the bonus granted by Stone Gaze.
Duration: Permanent
Duration: 4/5/6/7 ( 7/8/9/10)
Duration: 3/3.5/4/4.5
Duration: 6/7/8
Magical damage barrier[edit]
Magical damage barriers absorb a set amount of magical damage, no matter whether it comes from spells (magical spell damage) or attacks (magical attack damage). They absorb the damage before it is reduced by magic resistance, unless the resistance is provided by spell immunity. This means when a hero with for example 25% magic resistance and a 300 health damage barrier gets hit by 400 magical damage, the shield will absorb 300 of that. The exceeding 100 are not absorbed and are now reduced by the 25% magic resistance down to 75. So in this scenario, the hero takes 75 damage. This means a barrier is more effective the lower a unit's magic resistance is, similar to how damage block is more effective, the lower the armor is.
Multiple sources of magical damage barriers do not stack. When affected by multiple, all of them deplete at the same time. For example, if a unit is affected by a level 4 Flame Guard (500 barrier health) and by Pipe of Insight (400 barrier health), and then takes 300 magical damage, both shields lose 300 capacity, leaving Flame Guard with 200 and Pipe of Insight 100 absorb capacity.
Sources of magic damage barriers[edit]
Barrier Health: 80/220/360/500 ( 280/420/560/700)
Duration: 8/12/16/20- Barrier Health: 325
Duration: 12 - Barrier Health: 400
Duration: 12
See also[edit]
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