Ability Power or Magic Peneration?

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BeefJerkyHunter

Senior Member

02-08-2010

Hey, I was wondering for caster users especially of which is better to get.
Let's take two items for example.
Let's compare the Haunted Guise and Fiendish Codex (due to similar costs).
Now here is where I'm wondering if Magic Penetration would out do more Ability Power.

Would you do more damage with getting +20 magic penetration or with 30 Ability Power?

And then, if you were to upgrade the Fiendish Codex to a Nashor's Tooth, would the 55 ability power be better than the +20 magic penetration?

So yeah, magic penetration or ability power?


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wildfire393

Senior Member

02-08-2010

In general, Magic Penetration is better for casters who have overall low AP Ratios, such as Annie (whose ratios are all around .6) and Fiddlesticks (whose per-hit ratios are fairly low, despite having high ratios when you total all of the hits/ticks of his attacks). People who have high AP Ratios (Nunu, Sion, etc) or abilities which do not deal damage but still scale with AP (Morgana, Soraka) benefit more from AP.

Keep in mind also, the more damage your abilities do, the more that MPen increases your damage by.

If you do 100 damage against someone with 50 MR (1/3rd reduction), your damage is ~66. With 20 Magic Penetration, your damage goes up to 76 (an increase of 10)

If you do 200 damage in the same situation, your damage is 133, and with 20 magic penetration, it goes up to 154 (an increase of 21).

Of special note is the Void Staff, which does a percentage magic penetration, meaning that its relative increase to your damage actually scales with how much MR the enemy has.