Binding of Isaac: Rebirth Wiki
Added in Afterbirth

Damage scaling is a mechanic introduced in The Binding of Isaac: Afterbirth to make certain monsters and bosses more challenging, enabling some enemies to retaliate against high damage attacks by utilizing armor, which caps Isaac's damage per second to a max amount. The more damage dealt to such an enemy in a short period of time, the more Isaac's damage gets reduced.


  • The armor is based on 4 different criteria: how much base HP the entity has, how much damage it has taken in the last 4 seconds (120 game logic frames), the value of its armor (every applicable entity has a specific armor value), and their starting armor protection (increases from a value of 0 to 120).
  • Every entity in the game is predisposed to make use of this mechanic: in fact, every entity sports a "starting armor protection" counter and an "armor value" field, but few entities actually use it.

How it Works[]

  • When an entity with an armor value spawns, it starts off with a separate instance of armor. This instance of armor starts off by reducing incoming damage by 99%, and will steadily decrease over the course of 4 seconds at which point it is no longer in effect. This value will increase its "armor deployment" each game logic frame going from 0 (fully armored) to 120 (no longer in effect), and use this value to compute a 'static degree' of damage reduction, separate from this starting armor protection.
    • Added in Afterbirth † In practice, this is only a significant factor in the battle with Delirium Delirium, as while it's transformed, its starting armor protection is reapplied. In the cases of all other armored entities, the starting armor protection becomes irrelevant after 4 seconds.
  • The entity keeps track of how much unmodified damage it has taken in the last 4 seconds, which combined with the 'static degree', the entity's HP, and armor effectiveness results in a multiplier to the actual damage dealt, capping out at a multiplier of 0.09x (in other words, Isaac's tears can never deal less than 9% of his Damage stat). This can stack with the starting armor protection to reduce damage even further.
  • The entity's base HP is divided by its armor value to create a soft cap on damage per second (DPS). This soft cap serves as a way to equalize damage coming from Isaac; if his DPS is above this cap, it will be lowered, while DPS values below the soft cap are completely unaffected. The higher Isaac's DPS, the more his damage will be decreased.
  • Due to the entity keeping track of how much unmodified damage it has taken in the past 4 seconds, Isaac's damage output will gradually decrease until it is equalized to the DPS soft cap, or the damage instance reaches the point that it is reduced to 9% of its original damage.
  • Isaac's Damage stat is also taken into consideration, not just his DPS. If an individual damage instance is greater than 4 times the armored entity's DPS soft cap, that damage will be preemptively decreased, so as to prevent Isaac from obliterating entities in one shot, even if the entity has not been attacked in a period of 4 seconds.
  • The overall result of this mechanic is that slow, high-powered attacks are less effective than rapid, lower damage ones; the damage reduction formula has difficulty keeping up with rapid, low damage attacks while slow, high-powered attacks will preemptively have their damage lowered, allowing for such attacks to have their damage equalized more easily.
  • Ultimately this mechanic has its limits, as no matter what, each individual attack cannot have its damage reduced below 9% of its original damage, allowing the armor to be overwhelmed if the outgoing damage per second is large enough.

Added in Repentance Bypassing Damage Scaling[]

  • Methods were added to bypass this mechanic, giving Isaac ways to deal full damage by certain means. These ways of dealing damage however do contribute to Isaac's damage per second, which can cause the damage dealt from his other attacks to be lowered as a result of running into the DPS soft cap. The amount of damage dealt through these methods tend to outweigh the downsides of lowering Isaac's damage in most cases.
    • Bomb damage and most explosive damage in general bypasses damage scaling; most non-explosive bomb effects, however, do not (e.g. the tears fired by Sad Bombs Sad Bombs, etc).
      • Bomber Boy Bomber Boy: The initial explosion bypasses damage scaling, the subsequent explosions do not.
      • Ghost Bombs Ghost Bombs: The initial explosion bypasses damage scaling, the contact and explosion damage from the ghosts do not.
      • Scatter Bombs Scatter Bombs: Both the initial and subsequent explosions deal full damage.
    • Effects which invoke The Necronomicon The Necronomicon (e.g. Black Heart Black Hearts, XIII - Death XIII - Death, etc), and the damage boosts from A Missing Page A Missing Page and Missing Page 2 Missing Page 2 bypass damage scaling.
    • Knockback damage from Hemoptysis Hemoptysis and Knockout Drops Knockout Drops bypasses damage scaling.
    • Dark Esau (see Tainted Jacob Tainted Jacob) bypasses damage scaling with his charge attack.
    • Tick Tick bypasses damage scaling in all versions of the game.
  • The following items that deal explosive damage are exceptions and do not bypass damage scaling:

Entities with Armor Values[]

The game enables the armor for the following entities, one of which is only partial:

Entity HP Armor DPS Soft Cap
Hush Hush (first phase) 1,000 20 50
Hush Hush (second phase) 6,666 Removed in Repentance 160
Added in Repentance 140
Removed in Repentance 41.66
Added in Repentance 47.61
Ultra Greed Ultra Greed 3,500 85 41.18
Added in Afterbirth † Ultra Greedier Ultra Greedier 2,500 Added in Afterbirth † / Removed in Repentance 85
Added in Repentance 60
Added in Afterbirth † / Removed in Repentance 29.41
Added in Repentance 41.67
Added in Afterbirth † Delirium Delirium (While transformed) 10,000 Up to 80 (see notes) Up to 125 (see notes)
Added in Repentance The Beast The Beast 10,000 60 166.67
Added in RepentanceBlood Puppy Blood Puppy (Level 2) 20 90 0.22
Added in RepentanceBlood Puppy Blood Puppy (Level 3) 50 90 0.56
Added in Repentance Dogma Dogma 2,400 30 80
Added in Repentance Elleech Elleech 60 5 12
Added in Repentance Gutted Fatty Gutted Fatty 80 12 6.67
Added in Repentance Level 2 Charger Level 2 Charger 40 2.5 16
Added in Repentance Level 2 Gaper Level 2 Gaper 40 5 8
Added in Repentance Level 2 Gusher Level 2 Gusher 20 2.5 8
Added in Repentance Level 2 Horf Level 2 Horf 20 2.5 8
Added in Repentance Mega Satan Mega Satan 5,000 90 55.56
Added in Repentance Mega Satan's Hands 600 15 40
Added in Repentance Mother Mother 4,222 90 46.91
Added in Repentance Shady Shady 80 12 6.67
Added in Repentance Tainted Boom Fly Tainted Boom Fly 20 10 2
Added in Repentance Tainted Faceless Tainted Faceless 100 20 5
Added in Repentance Tainted Hopper Tainted Hopper 80 30 2.67
Added in Repentance Tainted Mole Tainted Mole 80 10 8
Added in Repentance Tainted Mulligan Tainted Mulligan 100 30 3.33
Added in Repentance Tainted Pooter Tainted Pooter 75 30 2.5
Added in Repentance Tainted Round Worm Tainted Round Worm 100 30 3.33
Added in Repentance Tainted Soy Creep Tainted Soy Creep 50 4 12.5
Added in Repentance Tainted Spitty Tainted Spitty 60 30 2
Added in Repentance Tainted Sub Horf Tainted Sub Horf 50 8 6.25
Added in Repentance Tainted Sucker Tainted Sucker 14 10 1.4
Added in Repentance Tainted Tube Worm Tainted Tube Worm 120 12 10
Added in Repentance Ultra Death Ultra Death 2,000 30 66.67
Added in Repentance Ultra Famine Ultra Famine 2,000 30 66.67
Added in Repentance Ultra Pestilence Ultra Pestilence 1,800 30 60
Added in Repentance Ultra War Ultra War 2,000 30 66.67


  • Added in Afterbirth † Delirium Delirium only has armor while assuming the form of random bosses. Its armor will start from 0 and increase as damage is taken while transformed; once taking the shape of its true form, it won't have any. Its armor only protects its alternate forms. Every time Delirium transforms, it's partial armor will be reapplied, resulting in considerably more damage reduction than the armor value alone.
  • Armor is always actively updated, not only when an entity is taking damage.
  • It is possible to apply the armor effect to any entity via editing its entry in entities2.xml.
  • Midas' Touch Midas' Touch will lessen Ultra Greed's armor effectiveness by 25%.


  • Despite the armor attempting to balance damage dealt and keep fights challenging, it's very possible to overwhelm the mechanic and destroy even strong armored enemies like Hush Hush.