Penetration

Penetration is a base statistic in Predecessor. It's divided into Physical Penetration and Magical Penetration, which respectively penetrate Physical and Magical Armor.

Penetration is the calculation that determines how much of a Hero's Damage will go through an enemies Defense, which is determined by their Physical Armor. This is split into two similar but very distinct categories, Flat Penetration (FP) and Percent Penetration (%P).

In Predecessor, penetration is calculated as armor reduction. The formula for a character's effective Armor after Penetration is:

Effective Armor = ((Armor Value - Armor Reduction) * (1 - Percent Penetration) - Flat Penetration)

Example: If you have 200 armor and get attacked by a Hero with Basilisk (24% Armor Reduction) and Demolisher (28% Percent Penetration and 6 Flat Penetration), you will have ((200-24%)*(1-28%)-6)=103.44 Effective Armor against that Hero.

Flat Penetration

Flat penetration (Also known as Lethality) is the statistic which can be acquired from items, crests, and abilities such as Wraith's Surprise, Surprise!. Flat penetration is applied after Percentage Penetration.

Percentage Penetration

Percentage penetration (also called Armor Ignore) can only be acquired from items such as Demolisher, The Perforator and Caustica, which have passives associated with giving percentage penetration to your Hero once bought. It's applied after Armor Shred, but before Flat Penetration.

Armor Shred

Armor Shred (or Armor Reduction), unlike Flat Penetration and Percentage Penetration, is a temporary debuff that reduces an enemy's Armor for a short duration and is applied before both Flat and Percentage penetrations. Unlike the other penetration types, Armor Shred can also be benefited from by the applier's teammates. There is two type of armor shred, percentage acquired from items such as Basilisk, and flat from item such as Deathstalker. Like penetration you apply first the percentage debuff and then the flat debuff.