Damage Scaling

Damage scaling is a mechanic introduced in The Binding of Isaac: Afterbirth to provide a more challenging experience to the players, enabling some enemies to retaliate against high damage attacks by deploying an "armor" of a sort. The more damage dealt to such an enemy in a short period of time, the more it gets reduced, offering an approach to keep the fight challenging and the difficulty high.

Overview

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), how effective its armor is (every entity has its unique value) and how deployed said armor is (from 0 to 120).

Every entity in the game is predisposed to make use of this mechanic: in fact, every entity sports an "armor deployment status" counter and an "armor value" field, but few entities actually use it.

How damage scaling works

When an "armor enabled" entity spawns, it'll increase its "armor deployment" each game logic frame going from 0 (no armor) to 120 (fully deployed), and use this value to compute a static degree of damage reduction. The entity keeps track of how much unmodified damage it has taken in the past 4 seconds, which combined with the static degree, the entity's HP and armor effectiveness results in a multiplier to the actual damage dealt.

Overall the formula results in slow, high-powered attacks being less effective than rapid, lower damage ones; the more damage sources put to work, the faster the entity's HP will go down, regardless of the raw amount of damage.

Entities and Their Armor Values

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

Entity	HP	Armor
Hush (first phase)	1,000	20
Hush (second phase)	6,666	160 140
Ultra Greed	3,500	85 85-170
Ultra Greedier	2,500	85 60
Delirium	10,000	(see below)
Mega Satan	5,000	90
Mega Satan's hands	600	15
Mother	4,222	90
Dogma	2,400	30
Ultra Famine	2,000	30
Ultra Pestilence	1,800	30
Ultra War	2,000	30
Ultra Death	2,000	30
The Beast	10,000	60
Gutted Fatty	80	12
Level 2 Gaper	40	5
Level 2 Horf	20	2.5
Level 2 Gusher	20	2.5
Level 2 Charger	40	2.5
Elleech	60	5
Shady	80	12
Tainted Pooter	75	30
Tainted Mulligan	120	30
Tainted Boom Fly	20	10
Tainted Hopper	80	30
Tainted Spitty	60	30
Tainted Round Worm	100	12
Tainted Tube Worm	120	30
Tainted Sucker	14	10
Tainted Soy Creep	50	4
Tainted Sub Horf	50	8
Tainted Faceless	100	20
Tainted Mole	80	10
Blood Puppy	20 / 50	30

Notes

• Delirium only has armor while assuming the form of random bosses. Its armor will start from 0 and increase with every damage taken while in "minion form" - once taking the shape of its true form, it won't have any. Its armor only protects its alternate forms.
• The armor is always actively updated, not only when the entity is taking damage. This makes it possible for the reduction multiplier to actually go above 1.0 after a period of not being hit, making the first attack after such a pause deal more damage than would be done without armor.
• It is possible to apply the armor effect to any entity using cheating/modding tools.

Trivia

• 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.
• Midas' Touch will lessen Ultra Greed's armor effectiveness by 25%.

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