# Penetration strategy

Once you have a firm grip on how each flavor of armor or magic penetration functions on the mathematical level, the next logical step would be to figure out which type of penetration will best suit your damage-dealing needs.

The following sentence is likely to either blow your mind, or seem very obvious:

**Percent penetration is most effective against tanks, flat penetration is most effective against squishies, and these two types of penetration should not be used together.**

If you’re reading this post in search of a hard-and-fast guideline to blindly follow for how to choose which type of penetration to build, take the above sentence and be on your way. If you’re interested in finding out why it’s is true, continue reading!

Note: the blue line is a REDUCTION in damage by armor. The red and green lines are damage BONUS from armor penetration, which can be thought of as a percent bonus applied as true damage.

## Percent penetration beats tanks

You’re playing a normal game. You select your champion, Ashe, and lock in. The game launches, and as all the players load, you notice the other team consists of five tanks.You’re filled with dread as you realize that all of their champions are capable of shrugging off your physical damage as if you weren’t even attacking.

Then, in a flash of brilliance, you remember that you know how to counter a high-armor target: percent penetration. Last Whisper (40% armor penetration). Every point of armor your target acquires as the game progresses directly boosts the effectiveness of that one item.

**The math:**

*Instead of thinking about this in terms of penetration, think of Last Whisper as an item that grants a percentage boost to your total physical damage that scales with the amount of armor on your target*. Against an individual target with X amount of armor, the percentage of bonus damage granted by (the armor penetration component of) this one item can be calculated as [AR(X) – AR(.6x)], where the function [AR(X) = X / (100 + X)] represents armor damage mitigation.

Still unsure why percent beats flat penetration against a tank? Read on, my friend!

## Flat penetration beats squishies

“He’s got a ton of magic resist, so I’ll build Haunting Guise and Sorcerer’s Shoes.”

No! No no no no no!!! NO! Bad! VERY BAD!

The idea of building flat magic penetration to counter a high magic resist target may seem to make sense at first glance, but when you analyze that decision a little bit further, you realize it’s an error.

The key is that armor and MR returns diminish, as depicted in my graph two posts ago. Each armor point is successively less important than the one before it, until the point where extra armor points do virtually nothing. Therefore, flat armor penetration against a low-armor target is negating critical armor points, where that same amount may add virtually no damage bonus against a high-armor target.

**The math:**

To calculate the bonus damage percent to a target with X armor from Y armor penetration, use [AR(X) – AR(X-Y)], where the function [AR(X) = X / (100 + X)] represents armor damage mitigation.

To illustrate, two examples:

1. You have 30 armor penetration. Your target has 50 armor. You deal 16.67% more damage because of armor penetration.

2. You have 30 armor penetration. Your target has 200 armor. You deal only 3.7% more damage from the armor penetration!

## There can only be one

In a game, you should avoid building both flat and percent penetration. Choosing to build both leads to a very inefficient build because flat penetration is calculated before percent penetration, creating an anti-combo. Every point of flat armor penetration reduces the scaling of your percentage armor penetration. Decide early who you’ll be targeting with your damage, and assess how much resistance they’ll likely have against it. For best results, pick either flat or percent penetration and forget about the other completely for the game.

**Penetration and You.**

Today, a friend asked me to explain to him how armor and magic penetration work, and a blog post seems the perfect way to do it! In the current state of the meta-game at level 30, team composition seems to be moving away from the traditional glass-cannon DPS champions defended by untouchable tanks toward more evenly distributed damage and toughness across the whole team (carry Ashe with Banshee’s Veil, tank Garen with Hexdrinker and Sunfire Cape, Rod of Ages on almost every AP carry?). To counter these tanky teams, a player needs to understand the role that armor and magic penetration play in their ability to deal damage.

**Two types of penetration**

(note, armor and magic penetration work the same)

**Flat Penetration: **Flat penetration reduces the effective amount of damage resistance your target has against your physical or magic damage. If penetration is displayed on an item, rune, or mastery without a percent sign, you can assume the amount is flat penetration. If you have X magic penetration and your target has Y magic resist, your magic abilities will do damage to that target as if they had Y-X magic resist instead.

**Percent Penetration: **Percent penetration reduces your target’s effective armor or magic resist by a percent of their total Armor/MR AFTER your flat penetration is applied. This kind of penetration is always denoted by a %. If you have X flat armor penetration and Y percent armor penetration, and your target has Z armor, your physical attacks do damage as if your target only had (Z-X) * Y% armor.

## Sources of penetration

**Flat Magic Penetration:** (runes) Greater Marks of Insight, Greater Quintessences of Insight, (items) Haunting Guise, Sorcerer’s Shoes, Malady.

**Percent Magic Penetration: **(items) Void Staff, (masteries) Archaic Knowledge.

**Flat Armor Penetration: **(runes) Greater Marks of Desolation, Greater Quintessences of Desolation, (items) Black Cleaver, Brutalizer, Youmuu’s Ghostblade, Stark’s Fervor, Sword of the Divine, (masteries) Sunder.

**Percent Armor Penetration: **(items) Last Whisper

For my first trick, I’ll show you a graph illustrating the relationship between Armor/MR and damage mitigation in League of Legends! This entry is simply to familiarize myself with WordPress’s image uploading process. 😀