# Damage Reduction

**Damage Reduction (DR)** is a stat that decreases damage received by the player or other NPCs based on a percentage. This is different from defense, which decreases damage by flat values. Each percentage point of DR is additive, incrementing a total value that the damage then gets decreased by.

## Player Damage Reduction

### Vanilla changes

The Calamity Mod adjusts the effective percentage of this stat for the player with a diminishing scale, with all DR reducing effects (such as Armor Crunch) being calculated after it has been scaled. NPC DR is not affected by this diminishing scaling.

The scaling formula is: 1 - ^{1}⁄_{(1 + dr)}

For example, if the player has 25% DR, it will be scaled to 1 - ^{1}⁄_{(1 + 0.25)} = 0.2, or 20% DR.

Defensive accessory modifiers now increase damage reduction:

- Hard increases DR by 0.25%.
- Guarding increases DR by 0.5%.
- Armored increases DR by 0.75%.
- Warding increases DR by 1%.

Items with their damage reduction values changed:

Item | Vanilla | Calamity | Note | |
---|---|---|---|---|

Ancient Iron Helmet | 0% | 3% | ||

Beetle Wings | 0% | 5% | ||

Frozen Turtle Shell | 25% | 15% | For the Ice Barrier buff. | |

Gold Chainmail | 0% | 5% | ||

Iron armor | 0% | 6% | ||

Iron Chainmail | 0% | 3% | ||

Iron Greaves | 0% | 3% | ||

Iron Helmet | 0% | 3% | ||

Lead armor | 0% | 4% | ||

Lead Chainmail | 0% | 2% | ||

Lead Greaves | 0% | 2% | ||

Lead Helmet | 0% | 2% | ||

Leaf Wings | 0% | 5% | While equipping a full set of Tiki armor. | |

Spectre Wings | 0% | 5% | While equipping the Spectre armor set with Spectre Hood. | |

Worm Scarf | 17% | 14% |

### List of Damage Reduction Boosts

#### Armor and accessories

Item | Damage Reduction | Notes | |
---|---|---|---|

The Community | +1.25% to 5% | Depending on bosses killed | |

Corrupt Flask | +4% | While in the Corruption | |

Crimson Flask | +4% | While in the Crimson | |

Archaic Powder | +5% | While Underground or in the Underworld | |

Baroclaw | +5% | ||

Giant Tortoise Shell | +5% | Disappears after taking damage for 5 seconds | |

Leviathan Ambergris | +5% | When dashing | |

Profaned Soul Crystal | +5% | At night or when submerged in water or honey | |

Shattered Community | +5% | ||

Victide Breastplate | +5% | ||

+10% | When submerged in liquid | ||

Wulfrum Jacket | +5% | ||

Wulfrum armor | +5% | When transformed | |

Fathom Swarmer Breastplate | +6% | ||

Fearmonger Plate Mail | +8% | ||

Bloody Worm Scarf | +10% | ||

Old Duke's Scales | +10% | While not exhausted | |

Tarragon Helm | +10% | ||

Tarragon Helmet | +10% | ||

Tarragon Horned Helm | +10% | ||

Tarragon Mask | +10% | ||

Tarragon Visage | +10% | ||

Gem Tech armor | +12% | While the pink gem is active | |

Rampart of Deities | +15% | When below 50% health | |

Reaver Helm | +15% | ||

The Sponge | +10% | When the barrier is active | |

Slagsplitter Pauldron | +10% | When dashing |

#### Buffs and debuffs

Item | Damage Reduction | |
---|---|---|

Moonshine | +3% | |

Spirit Defense | +3% | |

Hallowed Defense | +4% | |

Phantomic Shield | +5% | |

Regeneraga | +5% | |

Afflicted | +7% | |

Grax Boost | +10% | |

Irradiated | -10% | |

Corruption Effigy | -5% | |

Vulnerability Hex | -10% | |

Crumbling | -30% | |

Armor Crunch | -50% |

### Alternative Damage Reduction

**Alternative Damage Reduction** (**Alternative DR** or **ADR**) is a hidden player statistic separate from normal damage reduction. It directly modifies damage taken, and is affected differently by the scaling formula. The following tables show a list of damage reductions that are **additive** of each other, including sources inflicted to the player and external sources such as enemy debuffs.

#### Player Sources

Source | Damage Reduction | Contact | Projectile | Notes | |
---|---|---|---|---|---|

Abyssal Diving Suit | 0-15% | When damage taken is above 50 while the Abyssal Diving Suit Plates buff is active. Reduces by 3% as more hits are taken, up to three times where the plates are broken and DR reduces to 0%. | |||

Onyx Excavator Key | 10% | When moving over half of the mount's top speed while mounted. | |||

Tundra Leash | |||||

Snow armor | 10% | Only reduces damage taken from ice-based attacks. | |||

Trinket of Chi | 10% | After not being previously struck for 15 seconds. | |||

The Evolution | 15% | When struck by a projectile that has been previously reflected. | |||

Fearmonger armor | 15% | During the Pumpkin Moon or Frost Moon while no bosses are alive. | |||

Shield of the High Ruler | 15% | When struck by a projectile that faces the player. | |||

Aquatic Heart | 20% | While the Ice Shield buff is active. | |||

Phantomic Artifact | 20% | When struck with the Phantomic Bulwark active. | |||

Permafrost's Concoction | 30% | While the Encased buff is active. Effect has a 3-minute cooldown. | |||

Auric Tesla Royal HelmSet bonus | 50% | While the Tarragon Cloak set bonus buff is active. Effect has a 30-second cooldown. | |||

Tarragon HelmSet bonus | |||||

Auric Tesla Royal HelmSet bonus | 50% | While the Blood Frenzy set bonus buff is active. Effect has a 30-second cooldown. | |||

Bloodflare Ram MaskSet bonus | |||||

The Bee | 50% | When at full health with a 10-second cooldown. | |||

Flesh Totem | 50% | Effect has a 20-second cooldown. | |||

Daedalus HelmSet bonus | 50% | When reflecting a projectile. | |||

Lion Heart | 50% | When the energy shell is active while the weapon is held. | |||

The Transformer | 50% | Only reduces damage taken from electrical attacks and enemy bullets. A list of attacks can be seen here. | |||

Adrenaline Meter | 50-65% | When taking damage while the meter is full. Each of Adrenaline's permanent power-ups increases value by 5%, to a maximum of 65%. | |||

Corruption Effigy | -5% | While the player is in range. | |||

Vulnerability Hex | -10% | While the player is inflicted with this debuff. | |||

Irradiated | -10% | While the player is inflicted with this debuff. |

#### Non-Player Sources

Source | Damage Reduction | Contact | Projectile | Notes | |
---|---|---|---|---|---|

Profaned Weakness | 45% | While enemies are inflicted with this debuff. | |||

Temporal Sadness | 50% | While enemies are inflicted with this debuff. |

#### Calculation

After the total damage reduction is calculated, several effects may take place that will modify this stat:

- If the player is inflicted with Armor Crunch, the final value is multiplied by 0.5.
- If the player is inflicted with Crumbling, the final value is multiplied by 0.55.
- If the player has normal DR stat, the final value is multiplied by (1 - DR). The DR stat used is calculated
*after*being accounted for regular DR scaling. - After
*all*calculations, the final value is scaled using the same formula as the normal DR stat: 1 -^{1}⁄_{(1 + dr)}

For example, if a player receives **200** contact damage from an enemy inflicted by Temporal Sadness while under the effects of Armor Crunch, Bloody Worm Scarf, Corruption Effigy, and Endurance Potion.

- First, all sources of contact damage reduction are added, including Temporal Sadness and Corruption Effigy, totaling
`50% - 5%`

= 45%. - Next, the value is multiplied by Armor Crunch's multiplier, totaling
`45% * 0.5`

= 22.5%. - Then, the normal DR from Bloody Worm Scarf, Corruption Effigy, and Endurance Potion is accounted. The player's unscaled normal DR is
`7% + 10% - 5%`

= 12%, and final normal DR is`(1 - 1 / (1 + 0.12)) * 100%`

=**10.71%**. - Therefore, the alternative DR reduces to
`22.5% * (1 - 0.10714)`

= 20.09%. - Finally, the alternative DR goes through scaling and results in a final alternative DR of
`(1 - 1 / (1 + 0.2009)) * 100%`

=**16.73%**. - In the end, the player will take
`200 * (1 - 0.1071) * (1 - 0.1673)`

=**148**damage.

## Enemy Damage Reduction

Unlike player damage reduction, enemy damage reduction is a stat not available in vanilla, but rather added by the Calamity Mod to various NPCs including vanilla ones. Similar to the player, the enemy DR is calculated after defense.

Certain debuffs can reduce enemy damage reduction:

- Crumbling has a damage reduction multiplier of 0.92x.
- Armor Crunch has a damage reduction multiplier of 0.85x.
- Absorber Affliction has a damage reduction multiplier of 0.8x.
- Kami Flu has a damage reduction multiplier of 0.8x.
- Betsy's Curse has a damage reduction multiplier of 0.66x.
- Marked for Death has a damage reduction multiplier of 0.5x.

Certain enemies such as enraged Supreme Witch, Calamitas and the Dungeon Guardian have a 99.9999% damage reduction, effectively taking 1/1,000,000 of the original damage dealt. These enemies' damage reduction cannot be altered by any debuffs.

### List of NPCs with Damage Reduction

#### Calamity NPCs

#### Vanilla NPCs

### Reactive Damage Reduction

**Reactive Damage Reduction (Reactive DR or RDR)**, also known as **Timed Damage Reduction (Timed DR or TDR)** is a mechanic exclusive to Empress of Light during the day and Providence, the Profaned Goddess during the night. It is a mechanic that gives the boss extra damage reduction if the player appears to be dealing too much damage within the intended kill time. This DR gain is calculated after everything else, meaning it cannot be affected by debuffs.

This mechanic takes into account the time elapsed and the boss's health. The time elapsed is divided by kill time for the **Time Ratio** value, while the boss's current health is divided by its total health for the **Health Ratio** value. The Empress of Light and Providence have an intended kill time of 180 and 240 seconds respectively.

The damage reduction gained is based on a boss's Base DR, which is prior to any other effects such as debuffs. The total amount of damage reduction gained is equal to:

[(1 - Base DR) * 10] - ^{[(1 - Base DR) * 10]}⁄_{(2 - Time Ratio - Health Ratio)}

Reactive DR does not occur if the sum of Time Ratio and Health Ratio is greater than or equal to 1, or if the player is in Boss Rush.

For example, suppose night time Providence reaches 70% health within 46 seconds while she is inflicted with the Marked for Death debuff:

- Providence's base DR is 30% or 0.3.
- Providence's kill time value is 240 seconds. As such, the time ratio is equal to
`46 / 240`

= 0.19. - The health ratio is equal to 70% or 0.7.
- Therefore, the amount of reactive DR gained is equal to
`(1 - 0.3) * 10 -`

=^{(1 - 0.3) * 10}⁄_{(2 - 0.19 - 0.7)}`7 - (7 / 1.11)`

= 0.69 or**69%**. - Providence is also affected by Marked for Death, which multiplies damage reduction by 0.5x, from 30% to
**15%**. - The two values combine into a total, instantaneous damage reduction of
**84%**.

## Trivia

- The kill time-based Damage Reduction system is inspired by a similar mechanic from
*The Binding of Isaac: Rebirth*.

Game mechanics | |||||||||
---|---|---|---|---|---|---|---|---|---|

Combat | Damage Reduction • Defense damage • Enchantment • Hit sounds • Immunity frames • Lifesteal • Minions • Rogue | ||||||||

Environment | Biome backgrounds • Events • Music | ||||||||

Events | Acid Rain • Boss Rush | ||||||||

Game | Bestiary • Configuration options • Difficulty Modes (Death Mode • Revengeance Mode) • Fishing • Game controls • Lore • Secret world seeds (For the worthy • Get fixed boi) • Vanilla changes | ||||||||

Items | Alternative crafting ingredients • Charge • Consumable • Crafting stations (By Hand) • Drops • Modifiers • Rarity • Recipes • Vanilla item recipes | ||||||||

Player | Adrenaline Meter • Aggro • Buffs and Debuffs • Dash • Death prevention • Defense • Dodge • Flight Time Bar • Rage Meter | ||||||||

UI | Boss Health Bar • Cooldown Rack • Speedrun Timer • Status messages • Tips |