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Magic penetration

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Magic penetration (or spell penetration) is a champion statistic which allows the magic damage done from their abilities, enhanced attacks, etc. to ignore some or all of a target's magic resistance. All champions have 0 base magic penetration but can increase it with items, runes or abilities for a few champions. This cannot affect enemy magic resistance beyond 0 to deal bonus damage.

Magic resistance reduction is the effect of some items and champion abilities that temporarily reduces the magic resistance of one or more targets. This allows allies to benefit from the reduction of magic resistance. This can reduce magic resistance below 0, resulting in bonus damage (see Magic resistance).

Order of calculations

Magic penetration and magic resistance reduction work exactly like armor penetration and armor reduction.

Magic penetration and magic reduction are considered on the target champion in the following order[1]:

  1. Flat magic reduction
  2. Percentage magic reduction
  3. Percentage magic penetration
  4. Flat magic penetration

Preceding Preseason 3 Patch

  1. Percentage magic reduction
  2. Flat magic reduction
  3. Flat magic penetration
  4. Percentage magic penetration

Flat magic resistance reduction

Flat magic resistance reduction stacks additively.

Example: 20 magic resistance reduction reduces the target's magic resistance by 20, so a target with 30 magic resistance will be reduced to 10 magic resistance. (30 − 20 = 10)

Flat magic resistance reduction can reduce a target's magic resistance below zero. For example, if an enemy with 10 magic resistance has their magic resistance reduced by 25, the enemy will have −15 magic resistance.

Percentage magic resistance reduction

The target's magic resistance is multiplied by a percentage (100% − the listed reduction). Percentage magic resistance reduction stacks multiplicatively and is ignored if the target's magic resistance is 0 or less.

Example: 20% magic resistance reduction multiplies the target's magic resistance to 80%, so a target with 30 magic resistance will be reduced to 24 magic resist. (30 × 0.8 = 24)

Percentage magic resistance reduction makes a bigger difference on targets with higher magic resistance. For instance, with 40% magic resistance reduction, a target with 200 magic resistance will lose 80 while a target with only 50 magic resistance will lose 20.

Percentage magic penetration

The target's magic resistance is treated as being multiplied by a percentage for purposes of damage calculation (100% − the listed penetration). Percentage magic penetration stacks multiplicatively and is ignored if the target's magic resistance is 0 or less.

Example: 20% magic penetration causes the target to take damage as if its magic resistance was multiplied by 80%, so a target with 30 magic resistance will be treated as though it had 24 for purposes of damage calculation (the target's actual magic resistance value will not change, however).

Because the target's actual magic resistance value does not change, anything else depending on that value also doesn't change (e.g.  Galio's  Runic Skin).

Percentage magic penetration makes a bigger difference on targets with higher magic resistance. For instance, with 40% magic penetration, a target with 200 magic resistance will be considered as having 80 less while a target with only 50 magic resistance will be considered as having 20 less.

Flat magic penetration

The target's magic resist is treated as being reduced by an amount for purposes of damage calculation, but cannot be reduced below 0. Flat magic penetration stacks additively.

Example: 20 magic penetration causes the target to take damage as if its magic resistance was 20 less, so a target with 30 magic resistance will be treated as though it had 10 for purposes of damage calculation (the target's actual magic resistance value will not change, however).

Because the target's actual magic resistance value does not change, anything else depending on that value also doesn't change.

Examples

Given 20 flat magic resistance reduction and 30% magic resistance reduction, and the target is affected by 10 flat magic penetration and 40% magic penetration,

  • Target A has 80 magic resistance.
    • The 80 is reduced to 60 by the 20 magic resistance reduction.
    • The 60 is reduced to 42 by the 30% magic resistance reduction.
    • The 42 is considered to be 27.3 by the 35% magic resistance penetration.
    • The 27.3 is considered to be 17.3 by the 10 magic resistance penetration.
Target A takes damage as if it has 17.3 magic resistance.
  • Target B has 18 magic resistance.
    • The 18 is reduced to −2 by the 20 magic resistance reduction.
    • The −2 is not affected by any further calculations because it is less than 0.
      • Target B takes damage as if it has −2 magic resistance.

Graph of %increase in damage of mpen vs no mpen, at up to 300 MR:

Delucion MpenGraph

Increasing magic penetration

Items

  • Haunting Guise: Unique Passive - Eyes of Pain: +15 magic penetration. +25 ability power, +200 health. 1485 gold.
  • Liandry's Torment: Unique Passive - Eyes of Pain: +15 magic penetration. +50 ability power, +300 health. Unique Passive: Dealing spell damage burns enemies for 6% of their current health as magic damage over 3 seconds. If their movement is impaired, they take double damage from this effect. 2900 gold.
  • Sorcerer's Shoes: +15 magic penetration. Unique passive: Enhanced Movement 2. 1100 gold.
  • Void Staff: Unique Passive: +35% magic penetration.+70 ability power. 2295 gold.

Masteries

Note: Only the magic penetration bonus effect of these abilities is shown here. To read more information on each of these abilities, follow the link on each of them.

Runes

Neutral buffs

  • Crystal Scar's Aura grants every champion 5% magic penetration while playing on the Dominion game mode.

Reducing magic resistance

Items

  • Abyssal Scepter reduces the magic resistance of nearby enemy champions by 20.
  • Wit's End basic attacks reduce the target's magic resistance by 5 on hit, stacking up 5 times.

Champion abilities

Percentage reduction:

  •  Kog'Maw's  Caustic Spittle reduces the magic resistance of the target by 20 / 22 / 24 / 26 / 28% for 4 seconds.
  •  Trundle's  Subjugate reduces the magic resistance of his target by 20% and gains for the same amount. This amount is doubled over the next 4 seconds. The magic resistance reduction lasts for another 4 seconds after the drain completes.
  •  Jayce's  Transform: Mercury Cannon empowers his next auto attack to reduce the enemy's magic resist by 10 / 15 / 20 / 25% for 5 seconds.
  •  Karthus's  Wall of Pain reduces the magic resistance of all targets affected by 15% for 5 seconds.
  •  Kayle's  Holy Fervor allows her autoattacks against enemy champions reduces their magic resistance by 3% for 5 seconds. This debuff stacks up to 5 times.

Flat reduction:

  •  Amumu's  Cursed Touch passively makes his autoattacks reduce the magic resistance of enemies hit by 15 / 20 / 25 for 3 seconds.
  •  Fiddlesticks's  Dread passively reduces the magic resistance of nearby enemies by 10.
  •  Ryze's  Spell Flux reduces the magic resistance of all targets by 12 / 15 / 18 / 21 / 24 magic resistance reduction for 5 seconds.
  •  Soraka's  Starcall reduces the magic resistance of all targets by 6 (+1% AP) for 5 seconds, stacking up 10 times.

Notes

  • Magic penetration is a very valuable stat for casters. There are few sources for it and so Magic Penetration marks are very popular runes.
  • Since percentage penetration is applied before flat penetration, it is highly recommended to combine both statistics.
  • Commonly only one of Abyssal Scepter or Void Staff is built depending on how much magic resistance the enemy team is using.
  • Magic penetration not only affects all champion abilities that deal magic damage, but also affects magic damage items.
    • The actives on items like Deathfire Grasp benefit from magic penetration as well.

See also

References

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