Penetration, or “Pen”, comes in various forms and types. Like Damage and Defense, it is divided specifically into Basic and Ability.
- Base Pen, where you personally ignore an amount of your opponent’s Defense.
- Shred, where you lower an opponent’s Defense and they take more damage from any source (including your teammates).
- Steal, where you lower and opponent’s Defense while also increasing your own by the same amount.
- % Pen
- Flat Pen
- % Reduction
- Flat Reduction
The forms are important to know as what they do can affect how you play, the types are important as they are applied in a specific order and it alters how much damage you deal.
[Defense - (Flat Reduction + Flat Pen)] x [1 - (% Reduction + % Pen)] = FinalResistRating
In simple terms, using Flat Pen will alter the potency of % Pen. Flat Pen (like the bonus stat on Guard Piercer) never loses value, but having it or putting the effects of Gems like Shredding Strikes or Armor Aura on a target will reduce the effectiveness of a Gem like Piercing Basic.
To look at other ways one can take more/less damage you need to go back to the entire, complicated damage formula and pull out some key terms. The first of these goes right in line with everything just showed about Pen.
The simplified damage formula works in all cases unless your opponent has enough forms of Pen to completely remove your Defense Rating and still apply more Pen. In this case you are subject to something called “Negative Defense”, where you will take more damage than if you simply had a Defense Rating of zero.
The formula for Negative Defense is:
Health Lost = Damage Taken [1 + (1 - 0.99 ^ |Defense| )]