Whenever the character kills an enemy, all damage dealt exceeding the enemy's remaining hit points will be added as excess damage to the next shot (the Overkill shot). It doesn't matter how the enemy was killed (guns/melee/action skill/grenade/etc.), but the excess damage will only be added to the next gun shot, so the damage of melee strikes/grenades/etc. can't be increased by Overkill. If the next shot misses, all excess damage is lost.
Excess damage is preserved until the next shot is fired, regardless if the character switches weapons, reloads, does melee attacks, throws grenades, moves to another map or waits a long time.
Overkill "stacks" in the sense that if an enemy is killed with an Overkill shot, they may leave even more excess damage. The next (even more powerful) Overkill shot then may leave behind even more excess damage and so on – but this can't be exploited infinitely as there is a damage cap based on the gun damage of the weapon that fires the Overkill shot (not the weapon that killed the previous enemy).
Doing a critical hit on the Overkill shot will multiply the shot's entire damage, so it multiplies both regular damage and excess damage. Thus, critical hits should be scored to make the most of Overkill damage.
If several enemies are hit by splash damage, for example from a rocket, Overkill damage is applied to every enemy hit.
The damage an Overkill shot can deal is capped at 5x normal damage (the damage the shot would deal without any excess damage added).
OverkillMaxDMG = NormalDMG × 5
However, multi-projectile weapons suffer a penalty:
OverkillMaxDMG = NormalDMG × (1 + 4/N)
where N is the number of projectiles. Thus, the damage cap will be NormalDMG × 3 for a 2-pellet Atlas Q-System and NormalDMG × 1.4 for a 10-pellet shotgun. The more projectiles a weapon shoots, the worse its Overkill damage potential.
- This does not apply to weapons with "hidden" multiple projectiles that don't mention the "×N" number of projectiles in their Gun Damage specification, for example Lyuda or Bekah. They all have OverkillMaxDMG = NormalDMG × 5.
ExcessDMG = DamageDealt - HitPointsLeft
where DamageDealt is the number that pops up on the kill. Elemental modifiers don't matter in this formula because they are already included in DamageDealt. The exact number of hit points an enemy has left is usually unknown, but the general rule is that the fewer hit points the enemy had left, the higher the Excess Damage for the following Overkill shot.
- Multi-projectile weapons: If an enemy is killed with a multi-projectile weapon such as a shotgun, no more projectiles will hit the enemy than required for the kill; e.g. if an enemy with 160 health left is hit by a 100×5 shotgun, only two pellets will connect for 100×2 = 200 damage, so these weapons typically have lower Excess Damage potential. Generally, the higher the damage of a single projectile, the better for Excess Damage.
- Multi-kill: If a shot kills several enemies at once (e.g. with a rocket launcher), the game will use only one of those enemies for Excess Damage calculation, not all combined.
- Status effects: If an enemy dies from status effects such as burning, only the last number popping up will be used for Excess Damage calculation, which will usually be pretty low.
The overall damage of the Overkill shot is calculated thus:
OverkillDMG = NormalDMG + (ExcessDMG × (100% + GuardRank) × Element)
(Redundant brackets added to avoid misinterpretation)
- NormalDMG: the damage the shot would deal without any Excess Damage.
- GuardRank: the gun damage Guardian Rank is applied again to Excess Damage.
- Element: elemental modifier (e.g. 175% fire against flesh in Mayhem Modes and True Vault Hunter Mode). ExcessDMG doesn't preserve the element of the attack that killed the previous enemy, it adopts the element of the Overkill shot. Element isn't applied to NormalDMG in this formula because NormalDMG already includes this modifier.
Multi-projectile weapons such as shotguns will spread Excess Damage evenly among N projectiles:
OverkillProjectileDMG = NormalProjectileDMG + (ExcessDMG/N × (100% + GuardRank) × Element)
- This also doesn't apply to "hidden" multi-projectile weapons like Bekah or Lyuda – every projectile receives full Excess Damage, greatly improving their Overkill potential.
Status effects: The Overkill shot doesn't only increase impact damage, but also status effect damage. For example, if OverkillDMG is NormalDMG×3, then status effects are multiplied by ×3 too.
OverkillStatusDMG = NormalStatusDMG × OverkillDMG / NormalDMG
Notable weapons & gear
- Unforgiven: this pistol does over ×10 damage on critical hits, which also applies to Overkill damage – so on critical hits, it can turn little Excess Damage into huge overall damage. However, maximum damage is limited by its relatively low gun damage.
- Lyuda: The bullet spawns two additional projectiles after a short distance, each of which does full Overkill damage, greatly increasing Overkill potential.
- Bekah: The bullet spawns three additional projectiles after a short distance, each of which does full Overkill damage, greatly increasing Overkill potential. On top of that, on critical hits the projectiles may ricochet to another enemy, dealing full Overkill damage again.
- Antimatter Rifle: Fires a projectile that can hit multiple enemies if they are lined up. All damage is multiplied by x2, including Overkill damage, to every enemy hit. It is also elemental and does great status effect damage for even higher Overkill potential.
- Proton Rifle / Melter: Can be charged up to multiply all damage by ×2, including Overkill damage and status effects.
- ASMD: If the orb is hit by a bolt, does a big shock explosion with ×2.5 damage to every enemy hit. On an Overkill shot, it can deal massive damage to whole groups of shielded enemies. However, the explosion can't do critical hits.
- Projectile Recursion: The projectile ricochets several times, dealing full Overkill damage to every enemy hit, and it deals a huge amount of status effect damage. This weapon has extreme Overkill potential.
- Amplify shields: A +20% amplify shield multiplies NormalDMG by ×1.2, a Re-Router (+120%) by ×2.2. ExcessDMG is not affected, but since Overkill's damage cap is based on NormalDMG, maximum Overkill damage is increased by those amounts.
- Shotguns: Being multi-projectile weapons, they are inefficient for both gathering Excess Damage and for the Overkill shot for the reasons listed above.
- Maggie / Masher: Inefficient for the same reasons. Instead of ×5 OverkillMaxDMG of a single-projectile pistol, the Masher will have only ×1.8 max damage and the Maggie only ×1.67.
- Face-puncher: While it can deal a lot of damage, its Overkill potential greatly suffers from the same penalties as other shotguns. On top of that, it can't do critical hits, reducing Overkill potential even further.
- While all enemies hit by splash damage suffer Overkill damage, this does not apply to status effect damage. An enemy hit directly by the projectile suffers increased status effect damage, but enemies hit only by splash damage and not the projectile itself will suffer only the weapon's base status effect damage.
- Ghosts in Bloody Harvest will receive full damage from Overkill shots, but won't leave behind any Excess Damage. After killing a ghost, ExcessDMG is 0.