Armor

Armor is a mostly obscure stat present on both Survivors and monsters. Having positive armor reduces the damage that character takes, and having negative armor increases the damage taken. This damage modification applies to all damage taken, except for the damage from any hp-costing Interactables and damage from Survivors of the Void - DLC Content
Void Fog is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
Click for more info.Void Fog.

Damage taken is multiplied by $1-Armor/(100+|Armor|)$ . This is a number between 0 and 2.

If a character has positive armor:

• Damage taken is multiplied by $100/(100+Armor)$. This is a number between 0 and 1.
• The formula for the damage reduction is: $Armor/(100+Armor)$.

If a character has negative armor:

• Damage taken is multiplied by $2-100/(100-Armor)$. This is a number between 1 and 2. (Note that the negative armor is subtracted, and two negatives make a positive.)
• The formula for the damage increase is: $100/(100-Armor)-1$.

The armor value that modifies the damage is a sum of the following contributions:

• The value of the armor stat (base armor + modifications)
• +adaptive armor
• +300 if the character is an Empathy CoreEmpathy Cores
  Recruit a pair of Solus Probes that gain power with more allies.
  Every 30 seconds, summon two Solus Probes that gain +100% (+100% per stack) damage per ally on your team. and the incoming attack has the AoE damage flag

The modified damage is then decreased by 5 per stack of Repulsion Armor PlateRepulsion Armor Plate
Receive flat damage reduction from all attacks.
Reduce all incoming damage by 5 (+5 per stack). Cannot be reduced below 1.. Note that the final damage can never be less than 1.

Armor	Damage Reduction	Damage Multiplier
-100	-50%	1.5
-80	-44.44%	1.44
-60	-37.50%	1.38
-40	-28.57%	1.29
-20	-16.67%	1.17
-10	-9.09%	1.09
0	0.00%	1
1	1.00%	0.99
5	4.76%	0.95
10	9.09%	0.91
12	10.71%	0.89
15	13.04%	0.87
20	16.67%	0.83
30	23.08%	0.77
50	33.33%	0.67
70	41.18%	0.59
100	50.00%	0.5
200	66.67%	0.33
500	83.33%	0.17
1000	90.91%	0.09
5000	98.04%	0.02
10000	99.01%	0.01

Graph of damage multiplier for values of armor from -1000 armor to 1000 armor. It can be seen that negative armor slowly approaches 2x damage taken, while positive armor slowly approaches 0x damage taken.

It would take 330 Rose BucklersRose Buckler
Reduce incoming damage while sprinting.
Increase armor by 30 (+30 per stack) while sprinting. (+30 armor per stack while sprinting) to get a damage reduction of 99% while sprinting. This would amount to 9900 armor. Another way to achieve this amount of armor would be by obtaining 99 Survivors of the Void - DLC Content
Oddly-shaped Opal is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
Click for more info. Oddly-Shaped OpalsSurvivors of the Void - DLC Content
This content is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
Click for more info.Oddly-shaped Opal
Reduce damage the first time you are hit.
Increase armor by 100 (+100 per stack) while out of danger. to get the same damage reduction while out of combat.

Armor Modifications

Effects that increase a character's armor:

• Playing on Drizzle grants each player a hidden item which grants 70 armor.
• MercenaryMercenaryThe Mercenary is a high skill melee survivor that uses his many dodges to weave in and out of combat.
  Class: Unknown
  HP: 110 (+33 per level)
  Damage: 12 (+2.4 per level)
  Armor: 20
  Umbra: Hired Blade, REXREXREX is a half robot / half plant that uses HP to cast devastating skills from a distance. The plant nor the robot could survive this planet alone – but thankfully they have each other.
  Class: Unknown
  HP: 130 (+39 per level)
  Damage: 12 (+2.4 per level)
  Armor: 20
  Umbra: Symbiotes, LoaderLoaderThe Loader is a slow but powerful bruiser that can use her grappling hook to uniquely navigate the environment.
  Class: Unknown
  HP: 160 (+48 per level)
  Damage: 12 (+2.4 per level)
  Armor: 20
  Umbra: Bionic Powerhouse, AcridAcridAcrid is a melee-range hybrid who uses powerful poisons to melt tanky enemies.
  Class: Unknown
  HP: 160 (+48 per level)
  Damage: 15 (+3 per level)
  Armor: 20
  Umbra: Test Subject, Seekers of the Storm - DLC Content
  Seeker is part of the Seekers of the Storm DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info. SeekerSeekers of the Storm - DLC Content
  This content is part of the Seekers of the Storm DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info.SeekerAs a meditative mid-range brawler, Seeker utilizes powerful healing to sustain herself and her team.
  Class: Unknown
  HP: 115 (+34 per level)
  Damage: 12 (+2.4 per level)
  Armor: 20
  Umbra: Diviner of House Beyond, and Seekers of the Storm - DLC Content
  False Son is part of the Seekers of the Storm DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info. False SonSeekers of the Storm - DLC Content
  This content is part of the Seekers of the Storm DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info.False SonThe False Son is a slow but stalwart close-range warrior. With extreme health and defense, False Son can weather any storm. Use False Son's durability to stay in the fray and capitalize on his slow but deadly skills.
  Class: Unknown
  HP: 180 (+54 per level)
  Damage: 12 (+2.4 per level)
  Armor: 20
  Umbra: The Shattered Heir each have 20 base armor.
• MUL-TMUL-TMUL-T is an aggressive survivor who has the tools necessary for any job!
  Class: Unknown
  HP: 200 (+60 per level)
  Damage: 11 (+2.2 per level)
  Armor: 12
  Umbra: Right Tool for the Wrong Job has 12 base armor.
• MUL-T'sMUL-TMUL-T is an aggressive survivor who has the tools necessary for any job!
  Class: Unknown
  HP: 200 (+60 per level)
  Damage: 11 (+2.2 per level)
  Armor: 12
  Umbra: Right Tool for the Wrong Job Transport ModeTransport Mode (Utility)Heavy. Zoom forward, gaining 200 armor and 220% movement speed. Deals 250% damage to enemies.
  Survivor: MUL-T grants 200 armor while active.
• MUL-T'sMUL-TMUL-T is an aggressive survivor who has the tools necessary for any job!
  Class: Unknown
  HP: 200 (+60 per level)
  Damage: 11 (+2.2 per level)
  Armor: 12
  Umbra: Right Tool for the Wrong Job Power ModePower Mode (Special)Enter a heavy stance, equipping both your primary attacks at once. Gain 100 armor, but lose -60% movement speed.
  Survivor: MUL-T grants 100 armor while active.
• Rose BucklersRose Buckler
  Reduce incoming damage while sprinting.
  Increase armor by 30 (+30 per stack) while sprinting. grant 30 armor per stack while sprinting.
• Jade Elephant45sJade Elephant
  Gain massive armor for 5 seconds.
  Gain 500 armor for 5 seconds. grants 500 armor while activeElephant Armor Boost (Buff)
  Gain massive armor.Gain +500 armor, negating most attacks..
• Spinel Tonic60sSpinel Tonic
  Gain a massive boost to ALL stats. Chance to gain an affliction that reduces ALL stats.
  Drink the Tonic, gaining a boost for 20 seconds. Increases damage by +100%. Increases attack speed by +70%. Increases armor by +20. Increases maximum health by +50%. Increases passive health regeneration by +300%. Increases movespeed by +30%.
  
  When the Tonic wears off, you have a 20% chance to gain a Tonic Affliction, reducing all of your stats by -5% (-5% per stack). grants 20 armor while activeTonic Buff (Buff)
  Gain a massive boost to all stats.Gain the following boosts:
  +150% max health
  +150% max shield
  +170% attack speed
  +130% movement speed
  +20 armor
  +200% base damage
  +400% health regeneration.
• Irradiant PearlsIrradiant Pearl
  Increase ALL of your stats.
  Increases ALL stats by 10% (+10% per stack). increase base armor by 10% per stack.
• Survivors of the Void - DLC Content
  Oddly-shaped Opal is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info. Oddly-shaped OpalsSurvivors of the Void - DLC Content
  This content is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info.Oddly-shaped Opal
  Reduce damage the first time you are hit.
  Increase armor by 100 (+100 per stack) while out of danger. grants 100 armor per stack while out of danger.
• Survivors of the Void - DLC Content
  Void Fiend is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info. Void Fiend'sSurvivors of the Void - DLC Content
  This content is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info.Void FiendThe Void Fiend is a corrupted survivor that fluctuates between a controlled and corrupted form, each with different strengths and weaknesses. Managing this curse has become its fate.
  Class: Unknown
  HP: 110 (+33 per level)
  Damage: 12 (+2.4 per level)
  Armor: 0
  Umbra: Corrupted Amnesiac Void CorruptionVoid Corruption (Passive)At full Corruption, transform your abilities into more aggressive forms.
  Survivor: Void Fiend grants 100 armor while corrupted.

Boss Monsters have some base armor. See their individual pages for exact values.

• Clay Dunestrider'sClay Dunestrider
  Ravenous SymbiontHP: 2100 (+630 per level)
  Damage: 20 (+4 per level)
  Class: Ranged
  Speed: 9 m/s
  Armor: 20 life-draining tendrils grant the Dunestrider 200 armor while active.
• ScavengersScavenger
  Item HoarderHP: 3800 (+1140 per level)
  Damage: 4 (+0.8 per level)
  Class: Ranged
  Speed: 3 m/s
  Armor: 20 gain 200 armor while looking for an item.
• MithrixMithrix
  King of NothingHP: 1000 (+300 per level)
  Damage: 16 (+3.2 per level)
  Class: Melee / Ranged
  Speed: 15 m/s
  Armor: 20 gains 200 armor while performing his Shock Wave attack.

Effects that reduce a character's armor:

• The CrippleCripple (Debuff)
  Reduces armor by 20. Reduces movement speed by 50%. debuff reduces the victim's armor by 20.
• REX'sREXREX is a half robot / half plant that uses HP to cast devastating skills from a distance. The plant nor the robot could survive this planet alone – but thankfully they have each other.
  Class: Unknown
  HP: 130 (+39 per level)
  Damage: 12 (+2.4 per level)
  Armor: 20
  Umbra: Symbiotes Weaken/Natural ToxinsNatural Toxins (Passive)Certain attacks Weaken enemies hit, reducing their movement speed, armor, and damage.
  Survivor: REX reduces targets' armor by 30.
• Shattering JusticeShattering Justice
  Reduce the armor of enemies after repeatedly striking them.
  After hitting an enemy 5 times, reduce their armor by 60 for 8 (+8 per stack) seconds. inflicts PulverizedPulverized (Debuff)
  Reduce armor greatly.Reduces armor by 60., reducing targets' armor by 60.
• Survivors of the Void - DLC Content
  Symbiotic Scorpion is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info. Symbiotic ScorpionSurvivors of the Void - DLC Content
  This content is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info.Symbiotic Scorpion
  Permanently reduce armor on hit.
  100% chance on hit to reduce armor by 2 (+2 per stack) permanently. inflicts Survivors of the Void - DLC Content
  Permanent Armor Reduction is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info. Permanent Armor ReductionSurvivors of the Void - DLC Content
  This content is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
  Click for more info.Permanent Armor Reduction (Debuff)
  Permanently reduces armor.Reduces armor by 2 (2 per stack) for the remainder of the stage, or until killed.
  (stackable), reducing targets' armor permanently by 2 (+2 per stack) on every hit.

Adaptive Armor

MithrixMithrix
King of NothingHP: 1000 (+300 per level)
Damage: 16 (+3.2 per level)
Class: Melee / Ranged
Speed: 15 m/s
Armor: 20, the Survivors of the Void - DLC Content
Voidling is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
Click for more info. VoidlingSurvivors of the Void - DLC Content
This content is part of the Survivors of the Void DLC. It is only available if the DLC is enabled when starting a run.
Click for more info.Voidling
Diviner of the DeepHP: 2000 (+600 per level)
Damage: 15 (+3 per level)
Class: Ranged
Speed: 45 m/s
Armor: 20, and the Seekers of the Storm - DLC Content
False Son (Boss) is part of the Seekers of the Storm DLC. It is only available if the DLC is enabled when starting a run.
Click for more info. False SonSeekers of the Storm - DLC Content
This content is part of the Seekers of the Storm DLC. It is only available if the DLC is enabled when starting a run.
Click for more info.False Son (Boss)
HP: 1000 (+300 per level)
Damage: 18 (+3.6 per level)
Class: Melee
Speed: 14 m/s
Armor: 23 have the adaptive armor passive stat, which protect them against bursts of damage. Every time they take damage, they gain temporary armor equal to $3000\times (damage/maxHP)$, or 30 armor per 1% of the max HP dealt. This armor caps at 400 and decays at a rate of 40 per second.