Stage HP

Stage HP is a feature of some enemies, granting them extra health the higher the stage number they're encountered in is.

Calculation[]

The formula for an enemy's total health HP is $\color {white}{\mathit {HP}}={\mathit {BaseHP}}+\left(\mathrm {min} (4,{\mathit {Stage}})+0.8\times \mathrm {bound} (0,{\mathit {Stage}}-5,5)\right)\times {\mathit {StageHP}},$ where Base HP and Stage HP are the defined HP values for the given enemy and displayed in the enemies' pages, Stage is the current stage number as defined internally by the game and min and bound are functions that take the smaller of two values or bound the middle value between the two others respectively.

In practice, this means the enemy gains Stage HP extra health for the first 4 stages, gains nothing for stage 5, and then 4/5ths of Stage HP up to stage 10 after which their health stops increasing.

Chapters map to stage numbers as follows:

Stage number	Normal Mode	Greed Mode
1	Basement / Cellar / Burning Basement / Downpour / Dross I	Basement
2	Basement / Cellar / Burning Basement / Downpour / Dross II	Caves
3	Caves / Catacombs / Flooded Caves / Mines / Ashpit I	Depths
4	Caves / Catacombs / Flooded Caves / Mines / Ashpit II	Womb
5	Depths / Necropolis / Dank Depths / Mausoleum / Gehenna I	Sheol
6	Depths / Necropolis / Dank Depths / Mausoleum / Gehenna II	The Shop
7	Womb / Utero / Scarred Womb / Corpse I	Ultra Greed
8	Womb / Utero / Scarred Womb / Corpse II	-
9	???	-
10	Cathedral / Sheol	-
11	Chest / Dark Room	-
12	The Void	-
13	Home	-

Example[]

Consider a Dip with 3 base HP and 1 stage HP.

Basement I, i.e. stage 1: HP = 3 + (min(4, 1) + 0.8 * bound(0, 1 - 5, 5)) * 1 = 3 + (1 + 0.8 * 0) * 1 = 4
Womb II, i.e. stage 8: HP = 3 + (min(4, 8) + 0.8 * bound(0, 8 - 5, 5)) * 1 = 3 + (4 + 0.8 * 3) * 1 = 9.4
The Void, i.e. stage 12: HP = 3 + (min(4, 12) + 0.8 * bound(0, 12 - 5, 5)) * 1 = 3 + (4 + 0.8 * 5) * 1 = 11

Monsters and Bosses that use Stage HP[]

A total of 48 Monsters and 19 Bosses use this mechanic, with the Sins and Dark Esau counted among the latter group.

Name	ID	Base HP	Stage HP
Blue Gaper	297.0	30 16	2
Dump	876.0	10	1
Dump Head	876.1	10	1
Splasher	238.0	10	2
Tainted Sucker	61.7	14	1
Bulb	61.5	10	2
Bloodfly	61.6	6	1
Cloggy	872.0	15	2
Leper Flesh	310.1	5	1.5
Holy Mulligan	22.2	40	3
Tainted Mulligan	22.3	120	8
Clickety Clack	889.0	20	3
Eggy	29.2	20	2
Blister	303.0	16	8
Baby Begotten	883.0	18	3
Holy Eye	60.2	20	5
Swarm Spider	884.0	4.5	0.2
Butt Slicker	878.0	16	2
Planetoid	229.1	28	4
Baby Long Legs	206.0	16	4
Small Baby Long Legs	206.1	12	4
Crazy Long Legs	207.0	16	4
Small Crazy Long Legs	207.1	12	4
Vis Fatty	886.0	40	4
Fetal Demon	886.1	40	3
Dip	217.0	3	1
Big Corn	217.3	6	2
Drip	870.0	3	1
Wizoob	219.0	25 20	5 4
Red Ghost	285.0	25 20	5 4
Squirt	220.0	15	6
Dank Squirt	220.1	15	6
Splurt	871.0	15	6
Hardy	826.0	15	6
Black Maw	225.0	20	6
Skinny	226.0	10	4
Rotty	226.1	16	5
Crispy	226.2	12	4
Bony	227.0	8	2
Black Bony	277.0	8	2
Holy Bony	227.1	60	14
Gurgling	237.0	24	4
Grub	239.0	10	2.5
Polty	816.0	14	2.5
Ministro	305.0	9	2
Fly Trap	873.0	16	6
Flesh Maiden	880.0	24	4
Portal	306.0	9	5
The Headless Horseman	82.0	160	30
The Fallen	81.0	60	45
Krampus	81.1	60	45
Envy	51.0	40	7.5
Gluttony	49.0	60	15 20
Greed	50.0	60	15 20
Lust	47.0	60	15 20
Pride	52.0	60	15 20
Sloth	46.0	60	15 20
Wrath	48.0	60	24
Super Envy	51.1	60	7.5
Super Gluttony	49.1	60	15 25
Super Greed	50.1	60	24 30
Super Lust	47.1	60	24 30
Super Pride	52.1	60	24 30
Super Sloth	46.1	60	24 30
Super Wrath	47.1	60	24 30
Ultra Pride	46.1	85	15 25
Dark Esau	866.0	250	20

Trivia[]

The Monster with the lowest Stage HP (and with the lowest amount among all entities) is the Swarm Spider at 0.2, while the Monster with the highest is the Holy Bony with a staggering 14, nearly twice the amount of 2nd place. All other Monsters have an amount between 1 and 8.
The Boss with the highest Stage HP (and with the highest amount among all entities) is a tie between Krampus and The Fallen at 45. All other Bosses have an amount between 7.5 and 30.
All of the Seven Deadly Sins and Super Sins (save for Wrath, Envy, and Super Envy) had their Stage HPs buffed in repentance.
The Wizoob and Red Ghost are the only entities whose Stage HP were reduced in Repentance, both from 5 to 4.