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'''Damage Amplification''' or '''Damage Amp''' is a stat that multiplies the damage caused by the player to affected enemies and NPCs. It can be both positive and negative. In latter case it reduces damage and is also known as '''Damage Reduction'''.

{{#ev:youtube|apzBQPZyW_w|360|description=Video explaining Damage Amplification}}

== Calculation ==
Contrary to what the percentages might suggest, multiple sources of damage amplification do not all stack in the same way. There are three distinct categories of Damage Amplification, each interacting with the damage formula differently:

* '''Additive Amps:''' These add together with each other (including additive Damage Reductions) into a single pool.
* '''Multiplicative Amps:''' These multiply the total damage one by one.
* '''Instance Amps:''' These are nearly identical to multiplicative amps, main exception being they create a new instance of damage.

=== The Damage Formula ===

Based on testing, the generalized formula for how these amps apply to weapon damage is as follows:

<math>\text{Damage} = [(\text{Base Bullet Damage} \times \text{Weapon Multiplier}) \times (1 + \text{Total Additive Amps}) + \text{Flat Bonus}] \times \text{Multiplicative Amp}_1 \times \text{Multiplicative Amp}_2 \dots \times \text{Instance Amp Damage}_1 \times \text{Instance Amp Damage}_2</math>

'''Example:''' 

# A hero has a base bullet damage of '''100''' and '''0''' flat weapon damage for simplicity.
# The hero is affected by {{ItemIcon|Inhibitor}} (an Additive Damage Reduction of '''-30%'''). Their damage drops to '''70''' (100 * 0.70 = 70).
# {{HeroIcon|Ivy}} casts {{AbilityIcon|Air Drop}} on the hero (an Additive Amp of '''+20%'''). The additive pool is now -30% + 20% = -10%. The hero deals '''90''' damage (100 * 0.90 = 90).
# The hero parries an enemy hero (Multiplicative Amp of '''+25%''' against parried target''')'''. This is applied after the additive pool. The hero now deals '''112.5''' damage (90 * 1.25 = 112.5).

== Damage Amplification ==

=== Sources of Damage Amplification ===

==== Additive Amplifiers ====

{| class="wikitable sortable"
|+List of heroes
!Hero
!Ability
!Tier
!Stat change
|-
| rowspan="1" |{{HeroIcon|Calico}} 
| rowspan="1" |{{AbilityIcon|Ava}} 
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Ava|3|OutgoingDamagePercent}}%''' Ramping Damage Amp
|-
|{{HeroIcon|Ivy}}
|{{AbilityIcon|Air Drop}}
|0
|'''+20%''' Damage Amp on Ivy and carried ally
|-
| rowspan="2" |{{HeroIcon|Shiv}}
| rowspan="2" |{{AbilityIcon|Killing Blow}}
|0
|'''+{{#invoke:Abilities|get_ability_prop|Killing Blow|BuffDamage}}%''' Damage Amp
|-
|2
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Killing Blow|2|BuffDamage}}%''' Damage Amp
|-
|{{ItemIcon|Rebuttal}}
| -
| -
|'''+{{ItemData|Rebuttal|BonusDamagePercent}}''' Damage Amp
|}

==== Multiplicative Amplifiers ====

{| class="wikitable sortable"
|+List of heroes
!Hero
!Ability
!Tier
!Stat change
|-
| rowspan="2" |{{HeroIcon|Infernus}}
| rowspan="2" |{{AbilityIcon|Napalm}}
|0
|'''+{{#invoke:Abilities|get_ability_prop|Napalm|IncomingDamagePercentFromCaster}}%''' Damage Amp
|-
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Napalm|3|IncomingDamagePercentFromCaster}}%''' Damage Amp
|-
|{{HeroIcon|McGinnis}}
|{{AbilityIcon|Spectral Wall}}
|1
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Spectral Wall|1|BonusDamagePercent}}%''' Damage Amp
|-
|{{HeroIcon|Mo & Krill}}
|{{AbilityIcon|Scorn}}
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Scorn|3|DamageBonus}}%''' Damage Amp per Stack
|-
|{{HeroIcon|Victor}}
|{{AbilityIcon|Aura of Suffering}}
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Aura of Suffering|3|IncomingDamagePercent}}%''' Damage Amp
|-
|{{HeroIcon|Bebop}}
|{{AbilityIcon|Hook}}
|1
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Grapple Arm|1|BulletAmp}}%''' Weapon Damage Amp against hooked targets
|-
| All Heroes
| [[Parry]]
| 0
| '''+25%''' Damage Amp (Parried target takes 25% increased damage from all sources)
|}

==== Instance Amplifiers ====

{| class="wikitable sortable"
|+List of heroes and items
!Hero / Item
!Ability
!Tier
!Stat change
|-
| rowspan="2" |{{HeroIcon|Drifter}}
| rowspan="2" |{{AbilityIcon|Bloodscent}}
|0
|'''+{{#invoke:Abilities|get_ability_prop|Bloodscent|AmpDamagePercent}}%''' Damage Amp on Isolated Heroes
|-
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Bloodscent|3|AmpDamagePercent}}%''' Damage Amp on Isolated Heroes
|-
| rowspan="2" |{{HeroIcon|Lady Geist}}
| rowspan="2" |{{AbilityIcon|Malice}}
|0
|'''+{{#invoke:Abilities|get_ability_prop|Malice|VulnerabilityPerStack}}%''' Damage Amp per Stack
|-
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Malice|3|VulnerabilityPerStack}}%''' Damage Amp per Stack
|-
| rowspan="2" |{{HeroIcon|Paradox}}
| rowspan="2" |{{AbilityIcon|Pulse Grenade}}
|0
|'''+{{#invoke:Abilities|get_ability_prop|Pulse Grenade|DamageAmplificationPerStack}}%''' Damage Amp per Stack
|-
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Pulse Grenade|3|DamageAmplificationPerStack}}%''' Damage Amp per Stack
|-
| rowspan="2" |{{HeroIcon|Pocket}}
| rowspan="2" |{{AbilityIcon|Barrage}}
|0
|'''+{{#invoke:Abilities|get_ability_prop|Barrage|AmpPercentPerStack}}%''' Damage Amp per Stack
|-
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Barrage|3|AmpPercentPerStack}}%''' Damage Amp per Stack
|-
| rowspan="2" |{{HeroIcon|Sinclair}}
| rowspan="2" |{{AbilityIcon|Rabbit Hex}}
|0
|'''+{{#invoke:Abilities|get_ability_prop|ability_magician_animalhexarea|DamageAmpPercentage}}%''' Damage Amp
|-
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|ability_magician_animalhexarea|3|DamageAmpPercentage}}%''' Damage Amp
|-
|{{ItemIcon|Escalating Exposure}}
| -
| -
| '''+{{ItemData|Escalating Exposure|MagicIncreasePerStack}}''' Spirit Damage Amp per Stack
|}

==== Unique Amplifiers ====
These amplifiers have unique mechanics that do not cleanly fit into the Additive, Multiplicative, or Instance categories.

{| class="wikitable sortable"
|+List of heroes
!Hero
!Ability
!Tier
!Stat change
!Notes
|-
| rowspan="2" |{{HeroIcon|Billy}}
| rowspan="2" |{{AbilityIcon|Blasted}}
|0
|'''+{{#invoke:Abilities|get_ability_prop|Blasted|BulletDamageAmp}}%''' Bullet Damage Amp against wrecked enemies
| rowspan="2" | Post‑mitigation [[True Damage|true damage]] amp. (See [[#Bugs, Quirks, and Exceptions|Bugs section]].)
|-
|2
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Blasted|2|BulletDamageAmp}}%''' Bullet Damage Amp against wrecked enemies
|-
| rowspan="2" |{{HeroIcon|Celeste}}
| rowspan="2" |{{AbilityIcon|Radiant Daggers}}
| 0
|'''+{{#invoke:Abilities|get_ability_prop|Radiant Daggers|MagicIncreasePerStack}}%''' Spirit Damage Amp per Stack
| rowspan="2" | Functions like a multiplicative amp with additive bugs. (See [[#Bugs, Quirks, and Exceptions|Bugs section]].)
|-
|3
|'''+{{#invoke:Abilities|get_ability_upgrade_prop|Radiant Daggers|3|MagicIncreasePerStack}}%''' Spirit Damage Amp per Stack
|}

== Damage Reduction ==

'''Damage Reduction''' is a negative form of Damage Amplification, reducing the damage output of enemies or its user. Mechanically, standard Damage Reductions are treated as negative '''Additive Amps''' (see Calculation section).

=== Damage Reduction Stacking ===

Valve's May 22 patch notes state that Damage Reduction debuffs are intended to stack diminishingly (i.e., multiplicatively, in the same manner as Resistance)<ref>{{Update link|May|22|2026}}</ref>.

However, live testing confirms that standard Damage Reduction debuffs have not been fully migrated to this new system. Currently, Damage Reductions (such as {{ItemIcon|Inhibitor}} or {{AbilityIcon|Fire Scarabs}}) simply act as negative Additive Amps. This means they add directly together with other additive amps (positive or negative) rather than multiplying against each other.

=== Sources of Damage Reduction ===

==== Weapon and Spirit Reduction ====

{| class="wikitable sortable"
|+List of heroes
!Hero
!Ability
!Tier
!Stat change
|-
| rowspan="2" |{{HeroIcon|Mirage}}
| rowspan="2" |{{AbilityIcon|Fire Scarabs}}
|0
|'''{{#invoke:Abilities|get_ability_prop|Fire Scarabs|OutgoingDamagePenaltyPercent}}%''' Damage Reduction
|-
|3
|'''{{#invoke:Abilities|get_ability_upgrade_prop|Fire Scarabs|3|OutgoingDamagePenaltyPercent}}%''' Damage Reduction
|-
|{{HeroIcon|Silver}}
|{{AbilityIcon|Boot Kick}}
|3
| -35% Damage Reduction
|}

{{Item stat table|Damage Reduction}}

* {{ItemIcon|Cheat Death}}, {{ItemIcon|Golden Goose Egg}} and {{ItemIcon|Cursed Relic}} reduce damage dealt by its user.

==== Spirit Damage Reduction====

Spirit Damage Reduction from {{HeroIcon|Infernus}}'s {{AbilityIcon|Afterburn}} (T2) and {{ItemIcon|Silencer}} does '''not''' behave like standard Damage Reduction. Multiple sources of Spirit‑specific reduction stack additively with each other (e.g., Afterburn T2 + Silencer = sum of percentages). This combined spirit reduction is then applied as a '''separate multiplier''', multiplicative with all other additive amps such as {{ItemIcon|Inhibitor}}.
{| class="wikitable sortable"
|+List of heroes and items
!Hero / Item
!Ability
!Tier
!Stat change
|-
|{{HeroIcon|Infernus}}
|{{AbilityIcon|Afterburn}}
|2
|'''{{#invoke:Abilities|get_ability_upgrade_prop|Afterburn|2|OutgoingTechDamagePercent}}%''' Spirit Damage Reduction <br><small>'''Note:''' Additive with itself, but multiplicative with other additive amps.</small>
|-
|{{ItemIcon|Silencer}}
| -
| -
|'''{{ItemData|Silencer|TechDamageReduction}}''' Spirit Damage Reduction <small><br>'''Note:''' Additive with itself, but multiplicative with other additive amps.</small>
|}

== Bugs, Quirks, and Exceptions ==
* '''Additive Amps''' do not apply to many flat values, such as flat weapon damage bonuses, base damage for Melee abilities (Such as the bonus +60 damage from {{HeroIcon|Calico}}'s {{AbilityIcon|Leaping Slash}} T3 upgrade), {{ItemIcon|Capacitor}} active, {{AbilityIcon|Backstabber}}, etc.
* {{ItemIcon|Headhunter}}: Multiplicative non-instance amps are the only amps that work correctly with Headhunter damage.
* {{ItemIcon|Return Fire}}: Because Multiplicative Amps act as defensive stats on the target, if an attacker fires at a target with Return Fire while the attacker has an M-amp active against them, the attacker will take increased reflected damage.
* {{HeroIcon|Billy}}'s {{AbilityIcon|Blasted}} bullet amp is unique as it is a post-mitigation [[True Damage|true damage]] amp. Because of this, it does not work at all against barriers.
* {{ItemIcon|Silencer}} and {{HeroIcon|Infernus}}'s {{AbilityIcon|Afterburn}} Tier 2 Spirit Damage Reduction are exceptions to the standard Damage Reduction rule. They stack additively with themselves, but multiplicatively with other additive amps.
* {{HeroIcon|Celeste}}'s Spirit damage amp from {{AbilityIcon|Radiant Daggers}} works like a multiplicative amp but is affected by additive amp bugs (see the Additive Amps entry above).
* {{ItemIcon|Unstoppable}}: Suppresses all sources of Damage Reduction while active, but only for [[Spirit Damage]].
* Some abilities, such as {{AbilityIcon|Gutshot}}, are not impacted at all by Damage Reduction. More testing is needed to identify and confirm every exception.

==References==
<references/>

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