Most players that I see pick up Annie, or any mage for that matter just attempt to stack Ability power as high as possible. While this might be a valid tactic against a team of squishy carries, any competent team will be able to easily counter you with magic resist, especially with the current meta-game of "tanky DPS". For experienced players this guide is just stating the obvious, but not everybody knows these things.

This guide will explain how magic resist reduction/magic penetration work and will give examples of ideal levels of magic pen against various levels of magic resist so you can do the most amount of damage for your gold.

For this guide I will use the following abbreviations.
MR = Magic resist
MRR = Magic resist reduction
Mpen = Magic penetration
AP = Ability power

Please note that the items listed are just items that you should be always considering for Annie. This is not a build, this is a guide that focuses on magic pen. I'm in no way saying build all those items in a game, or to build them in the order listed.

The first important thing you need to know is how MR equates into damage reduction. MR works on a basis of diminishing returns, at lower levels the damage reduction per point of MR is at it's highest.

The actual equation (Taken from the LoL wiki) is



Doubling MR from 25 to 50 will give you the following

100 / (100+50) = 100 / 150 = 0.666 meaning all damage is reduced by 33%

Some other numbers of magic resist and their respective damage reduction values are as follows.

75 magic resist = 43% reduction
100 magic resist = 50% reduction
125 magic resist = 56% reduction

Between 80-90 is the point where further investment in MR for the sake of decreasing damage becomes pointless. Higher MR levels than this are strictly to counter any Mpen you have.

If you're still confused by this go to http://leagueoflegends.wikia.com/wiki/Magic_resistance for a more in depth explanation.

Quite simply 20 magic pen will lower their MR by 20. 40% Mpen will lower it by 40%. Same goes with MRR. The difference between the two is that MRR is applied before Mpen and can lower an enemies MR below 0 meaning you deal extra damage, Mpen cannot lower MR below 0.

The order of reductions are as follows.

MRR% -> MRR flat rate -> Mpen flat rate -> Mpen%.

For example, you have 0 MRR%, 20MRR, 40Mpen and 40% Mpen%, for an enemy with 100 MR... the 20MRR lowers it to 80, the 40Mpen then lowers it to 40 and the Mpen% lowers it to 24. Now you know the order of what type of magic pen takes place first you can work out what items to buy better.

As you can probably tell, mixing flat rate Mpen with Mpen% is not the most efficient way of doing things as Mpen% makes more of an impact the higher the MR they have. This is not to say you should never get both forms of Mpen, but just keep it in mind when considering buying that void staff.

Following my masteries and runes you should already have roughly 9Mpen and 15%Mpen. 99% of the time your lane opponent will have 30MR or around it to start with. So without even buying any items you will have their MR down to around 18 at the start reducing your damage by roughly 15%.

Sorcerers shoes
An early game sorcerers shoes here will be a huge help as it lowers their MR by 20, to pretty much 0 meaning you do almost true damage to anybody in the above mentioned scenario. That's right, your boots are now increasing your damage by 15% on all champions with the base 30MR, a significant amount better than 20% CDR which some people seem to opt for. Boots of Lucidity can be useful on certain casters such as Vlad for the increased lane sustainability, but for most casters you definitely want sorcerers.
TL;DR - Just get

Void staff
The 40%Mpen is great on high MR enemies. Along with Archaic knowledge you will have 55%Mpen, a scary amount. However, assuming you got sorcerers and are runed right you should have 29Mpen which factors in before the void staff. So you should only get one if either several of their team have MR's in the region of 80 upwards (Mpen from mentioned items will knock them down to around 25MR) or their tank just hates you and built 150MR upwards (Will take him down to 65). Note that if only their tank is building MR and has built an insane amount of it, say 200 don't even bother with the voidstaff, you won't knock it down to below the point where it makes a real difference, just let your AD take them.
TL;DR - Get if several champs with 80+MR or one between 120-175 MR.

Abyssal sceptre
Another flat 20 MR gone from your enemies. Along with sorcerers and runes this makes it 49Mpen. Worth getting if they have some light MR (Say mercury treads for example) but nothing really dedicated in MR. Also has some MR for yourself if they have an AP heavy team this can be a nice bonus. Plus this provides an aura, meaning your whole team can take advantage of the enemies lowered MR. If somebody on your team has one already, it's probably not a good idea you taking one as well.
TL;DR - Get if several enemies are around the 50-70MR area.


Overall. Always get sorcerers shoes. Get abyssal sceptre if they have moderate MR and void staff for high levels of MR.

For the following section lets assume that both ways to build use my runes, masteries, sorcerers shoes and a rabadons deathcap. Therefore at level 18, you have 164 AP, 29Mpen, 15% Mpen as a base for this. For the AP build I will also add second Rabadons and for the Mpen build I will add either a void staff or abyssal sceptre as appropriate. Rabadons is considerably more expensive than the Mpen items but it's the only straight AP option.

AP build : 319 AP, 29Mpen, 15% Mpen. These calculations will be shown in red.
Mpen void : 234 AP, 29Mpen, 55% Mpen. These calculations will be shown in blue.
Mpen Abyssal : 234 AP, 49Mpen, 15% Mpen. These calculations will be shown in green

The numbers below will show the damage done by Annies spells to champions with different levels of MR. The levels of MR will be 30/50/75/100/125
Disintegrate (260 damage + 60% of AP)
451/382/324/280/247
400/363/330/303/280
400/400/327/280/242

Things to take into account here. Rabadons costs the most gold out the three and Abyssal sceptre also offers you magic resist which is obviously still useful. Abyssal sceptre is also an aura and therefore your team can take advantage of it's effect as well. So it has more utility than it first appears. Take what you want from the numbers listed. Of course straight AP is going to be the most effective on enemies with low resistances and Mpen is best on enemies with high resistances. You need to look at what you're up against and keep track of what the enemy builds and counter it. At high level play the vast majority of people will get a Banshees Veil at some point, putting them up to at least 80 magic resist (Without mercury treads, runes or masteries) at which point magic pen clearly becomes the best choice.

I felt obligated to add this paragraph despite it not being completely on the topic of Magic pen. I cannot stress this enough, this item is amazing, especially for Annie, use it.

Its active removes a third of a champions current HP. With your already great burst it pretty much guarantees a kill unless you're trying to burst the tank. It's pretty much made for Annie, yet I very rarely see anybody pick it up.

I made this guide when I could not sleep at night because it gave me something to do. If there are any errors in terms of calculations or just general stupidity I blame it on the lack of sleep.

I know this guide is nothing ground breaking, but a lot of people ignore Magic pen entirely.