A stat modifier, for example, is "+50% Damage". While this mechanic is usually pretty straight forward, there are some pitfalls, and some not-so obvious details:
When a player/weapon has several different sources of a same modifier, they will combine additively to each other to create a grand total. This total can be either positive or negative.
- Grand Total: +175% Damage
- Recoil, for a weapon
- -50% Recoil from Barrel5
- +20% Recoil from Body2
- Grand Total: -30% Recoil
Note that the "additive" effect is only for a given stat. In particular, "WeaponDamage", "MeleeDamage", "BulletDamage" and "CriticalDamage" are all stats that grow independently. Because the final damage output is the multiplication of all these fields (when applicable), getting bonuses for each of these fields will yield exponential results.
- A character with "+50% weapon damage" mod, with a weapon with "+100% melee damage" weapon will melee for a total of 300% of the weapon's base damage.
- A character with "+15% Bullet Damage", and a Mod with "+80 Shotgun Damage" will strike foes with the shotgun for 1.15 * 1.80 = 207% of the weapon's base damage.
Once the grand total is calculated, it is applied as a whole to the corresponding value (and not 1 by 1): Having two +100% Damage modifiers will triple damage, not quadruple it.
If the total is positive, then it is straight up applied. For example, wielding a 100 damage gun and with a +175% Damage modifier, the gun will deal 100*(1+1.75) = 275 Damage.
When the total is negative, Borderlands uses another formula. Instead of directly applying the modifier, Borderlands applies it to a reciprocal function. For example, for a gun with a spread modifier of -130% from a barrel5, the modifier will be of 1/(1 + 1.3); if that gun had a base spread of 2, the final spread would be 0.87.
The rationale for this mechanic is to have the same scale of effect, regardless of the modifier's sign.
A notable list of stats that are affected by this rule are:
- Damage: Many weapon parts actually have negative bonuses.
- Spread: Very often breaks the -100% bar.
- Damage reduction: Brick's Juggernaut skill; Lilith's Silent Resolve and Resilience skills; Roland's Grit skill.
- -50% Damage Reduction => Player takes 66% Damage
- -100% Damage => Player takes 50% Damage
- Recoil: Internally, the game uses a "Recoil" stat, which it displays as its inverse, "Recoil Reduction"
Scope of the modifiers
Modifiers have two scopes: Gun and player. Basically, a gun will have its own internal modifiers, but these are invisible to the outside world. The gun will appear as a "base" to the player. The Player's modifiers will not mix with the gun's modifiers.