Magic Penetration vs Ability Power

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RIP Curse Voice

Member

08-06-2010

So I'd like to know once and for all which is better - Flat Magic Penetration or Ability power?

I'd heard that Magic Penetration beats AP stat-for-stat. If this is true, why do I see so many people with Ability Power glyphs/Quints when the Magic Penetration ones would be better?

I understand Ability power will increase other things aside from the amount of damage a spell does, such as the amount of damage a shield will absorb etc. But is it really enough to make a difference?

For instance, I just got out of a 5v5 match vs an AP Sion, and the guy was a beast. He had a Doran's ring and was at around 39 Ability power at level 1. I checked his rune page after the game (I lost) and he has AP Glyphs, 2 AP quints, and 1 magic pen quint. Now, I understand AP will increase the damage his shield will absorb, but is 29 extra damage absorbed/dealt really better than 3.8 Magic pen?

If someone could post why they prefer AP over Magic pen for runes I'd really like to hear it. Because thus far I'm kinda stumped.


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Azarhac

Senior Member

08-06-2010

AP quints and Magic penetration marks are the way to go tbh.


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RIP Curse Voice

Member

08-06-2010

Quote:
Originally Posted by Azarhac View Post
AP quints and Magic penetration marks are the way to go tbh.
But why not go all Magic pen marks with Magic pen quints?


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tannerface

Senior Member

08-06-2010

I only like ap runes for characters that heal so that I can have better healing early on.


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Elbo444

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Senior Member

08-06-2010

Quote:
Originally Posted by Hyco View Post
But why not go all Magic pen glyphs with Magic pen quints?
first of all you want magic pen marks, not glyphs

second AP gives Sion's shield defense as well as offense, it's really just preference I think, do you want it to do more damage when it explodes or have it tank more damage


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Skwid1g

Senior Member

08-06-2010

I'd prefer penetration assuming I'm not getting Void Staff early.

Did he rush Lichbane? He might've figured that AP > Mpen with Lich Bane, or he may have had that rune page for a healer, or maybe he just didn't know mpen > AP for damage rune wise.


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noskill5

Senior Member

08-06-2010

Quote:
Originally Posted by Hyco View Post
But why not go all Magic pen glyphs with Magic pen quints?
Ok some basic theorycrafting. Lets assume a .8 ratio, on a single target spell. Flat AP quints x3 will immediately add approximately 12 damage for each cast, whereas MRPen quints will effectively ignore a certain amount of the MR. Hence, you'd expect an increase in both base, and AP bonus damage. The nature of MRPen is that it is only superior when the amount of damage increase provided by it is superior than the amount of AP multiplied by its respective ratio. Thus, in this case, you'd need an increase of 12 damage for it to be worthwhile, before MR. How much is that? Keep in mind MRPen makes it effectively calculate your targets MR to be lower by that amount.

let damage = d, base spell damage = b, magic resistance = MR = 30 (base), and MRPen
damage reduction via MR = MR/(MR+100)
Thus dmg received equals (1-[MR/(MR+100)]) multiplied by the amount of damage of the spell cast. Assuming the MRPen equals 3*1.96 (ie. the amount received from 3 quints)

Firstly, flat AP quints provide 12 bonus damage, assuming a .8 ratio, thus, you'd deal 12*(1-[30/(30+100)]) = 9.2 damage additional.

The additional damage due to MRpen equals the damage taken after applying it minus the damage taken before applying it

9.2 = b(1-(30-1.96*3)/(130-1.96*3))-(1-(30/130))

b = 9.2/((1-(30-1.96*3)/(130-1.96*3))-(1-(30/130)))

Thus, with a .8 ratio on the spell, you'd require the base damage to be greater than or equal to 252 before MRPen quints will provide additional damage. This isn't including any bonus to damage through AP glyphs or, well, any source.



To put this all into perspective, you need to consider the amount of AP bonus you will have, and when you will need the most damage. The bottom line is, flat AP provides you with a hefty amount of bonus damage at the lower levels, and MRPen doesnt start scaling better until after the first 15 minutes or so. This bonus damage helps an exceeding amount early game, which is when most games are decided, hence most players decide to go with flat AP quints over MRPen quints. If you will quickly get more AP, MRPen starts to shine very fast.


Note: I havent double checked all that math and I just pulled an all-nighter, so it may be off. If someone wants to confirm or refute either way it would be appreciated.


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IS186afbf367d955

Senior Member

10-20-2010

I did the mathcrafting a while ago on kassadin and they were about the same. But in some cases AP Quints are better. For instance with morgana it allows me to fullly kill a caster creep wave with lvl 3 tormented soil, it also improves black shield. If your character has a heal, AP quints are also usually better than mpen quints.


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Contralize

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Senior Member

10-20-2010

I'd think i prefer mpen for better early game


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Selomorbos

Senior Member

03-15-2011

Magic pen works on almost every character in the game as even most pure physical damage champions do some sort of magic damage. AP only really works on champions that have good ratios. I personally would suggest starting with magic pen, if your looking to buy. AP is just better sometimes, and works well if your making lichbane, which i dont see often but to be honost i think lichbane is a sleeping item.


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