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 52 Monsters and 18 Bosses use this mechanic, with the Sins counted among the latter group.

Name	ID	Base HP	Stage HP
Baby Begotten	883.0	18	3
Baby Long Legs	206.0	16	4
Big Corn	217.3	6	2
Black Bony	277.0	8	2
Black Maw	225.0	20	6
Blister	303.0	16	8
Bloodfly	61.6	6	1
Blue Gaper	297.0	30 16	2
Bone Fly	25.4	8	3
Bony	227.0	8	2
Boom Fly	25.0	8	3
Bulb	61.5	10	2
Butt Slicker	878.0	16	3
Clickety Clack	889.0	20	3
Cloggy	872.0	15	2
Crazy Long Legs	207.0	16	4
Crispy	226.2	12	4
Dank Squirt	220.1	15	6
Dip	217.0	3	1
Dragon Fly	25.3.0	8	3
Dragon Fly X	25.3.1	8	3
Drip	870.0	3	1
Drowned Boom Fly	25.2	8	3
Dump	876.0	10	1
Dump Head	876.1	10	1
Eggy	29.2	20	2
Fetal Demon	886.1	40	3
Flesh Maiden	880.0	24	4
Fly Trap	873.0	16	6
Grub	239.0	10	2.5
Gurgling	237.0	24	4
Hardy	826.0	15	6
Holy Bony	227.1	60	14
Holy Eye	60.2	20	5
Holy Mulligan	22.2	40	3
Leper Flesh	310.1	5	1.5
Ministro	305.0	9	2
Planetoid	229.1	28	4
Polty	816.0	14	2.5
Portal	306.0	9	5
Red Boom Fly	25.1	8	3
Red Ghost	285.0	25 20	5 4
Rotty	226.1	16	5
Sick Boom Fly	25.5	8	3
Skinny	226.0	10	4
Small Baby Long Legs	206.1	12	4
Small Crazy Long Legs	207.1	12	4
Splasher	238.0	10	2
Splurt	871.0	15	6
Squirt	220.0	15	6
Swarm Spider	884.0	4.5	0.2
Tainted Mulligan	22.3	120	8
Tainted Sucker	61.7	14	1
Vis Fatty	886.0	40	4
Wizoob	219.0	25 20	5 4
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	40	7.5
Super Gluttony	49.1	60	15 25
Super Greed	50.1	60	15 25
Super Lust	47.1	60	15 25
Super Pride	52.1	60	15 25
Super Sloth	46.1	60	15 25
Super Wrath	48.1	60	24 30
Ultra Pride	46.2	85	15 25

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.
• The Wizoob and Red Ghost are the only entities whose Stage HP were reduced in Repentance, both from 5 to 4.

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