Bosses

Bosses are very strong monsters found in boss rooms at the end of a floor. The boss at the end of the floor must be defeated in order to advance to the next floor. In later chapters, bosses are able to spawn as normal enemies. This starts in the caves, where the Gurglings are often encountered. The boss for a particular floor is chosen from the pool of bosses for the environment of the floor. Bosses may also spawn as champions, which can change various attributes such as health, damage, and attack pattern. Upon defeat, most bosses will drop an item from the boss item pool.

Bosses boast additional resistances to status effects. For example, fear occurs less often and the Night Light is unable to slow them down.

Additionally, some floors may spawn a room with a Mini-Boss.

Chapter 1

The Basement

Monstro	Gemini	Larry Jr.

Dingle	Gurglings	Steven

The Cellar

Pin	Widow	Blighted Ovum

Fistula	Gurdy Jr.	The Haunt

The Basement and The Cellar

The Duke of Flies	Famine	Rag Man File:DLC Indicator.png

Little Horn File:DLC Indicator.png	Dangle File:DLC Indicator.png	Turdlings File:DLC Indicator.png

Burning Basement File:DLC Indicator.png

Rag Man File:DLC Indicator.png	Little Horn File:DLC Indicator.png	Dangle File:DLC Indicator.png

Turdlings File:DLC Indicator.png

Chapter 2

The Caves

Chub	Gurdy	Mega Maw

Mega Fatty	C.H.A.D.	Rag Mega File:Afterbirth† Indicator.png

The Catacombs

The Hollow	The Husk	Dark One

Polycephalus	Carrion Queen	The Wretched

The Caves and The Catacombs

Peep	Gurdy Jr.	Pestilence

The Frail File:DLC Indicator.png	The Stain File:DLC Indicator.png	The Forsaken File:DLC Indicator.png

Big Horn File:Afterbirth† Indicator.png

Double Trouble

(Double Trouble) Dingle	(Double Trouble) The Duke of Flies	(Double Trouble) Gemini

(Double Trouble) Widow	(Double Trouble) Pin	(Double Trouble) Polycephalus

(Double Trouble) Larry Jr.	(Double Trouble) Blighted Ovum	(Double Trouble) Monstro

Flooded Caves File:DLC Indicator.png

The Frail File:DLC Indicator.png	The Stain File:DLC Indicator.png	The Forsaken File:DLC Indicator.png

Big Horn File:Afterbirth† Indicator.png

Chapter 3

The Depths

The Cage	Monstro II	The Gate	Gish

Necropolis

The Adversary	The Bloat	Mask of Infamy

The Depths and Necropolis

Loki	War	Brownie File:DLC Indicator.png

Sisters Vis File:Afterbirth† Indicator.png

Double Trouble

(Double Trouble) Gurdy Jr.	(Double Trouble) The Haunt	(Double Trouble) The Wretched	(Double Trouble) The Husk

(Double Trouble) Peep	(Double Trouble) Mega Fatty	(Double Trouble) Dark One

(Double Trouble) Mega Maw	(Double Trouble) Larry Jr.	(Double Trouble) Blighted Ovum

Dank Depths File:DLC Indicator.png

Brownie File:DLC Indicator.png

The Depths, Necropolis and Dank Depths

Mom

Chapter 4

The Womb

Mr. Fred	Scolex

Utero

Mama Gurdy	Lokii

The Womb and Utero

Blastocyst	The Bloat	Daddy Long Legs

Teratoma	Triachnid	Death

Conquest

Double Trouble

(Double Trouble) The Cage	(Double Trouble) Gurdy	(Double Trouble) The Fallen	(Double Trouble) The Gate	(Double Trouble) Loki

The Womb, Utero and Scarred Womb

Mom's Heart	It Lives

Blue Womb File:DLC Indicator.png

Hush File:DLC Indicator.png

The Void File:Afterbirth† Indicator.png

Delirium File:Afterbirth† Indicator.png

Chapter 5

Sheol

Satan

The Cathedral

File:Boss Isaac (Boss).png

Isaac

Chapter 6

The Chest

???

Dark Room

The Lamb

Golden Door Boss

Mega Satan

Universal

Universal Bosses are those which may appear at the end of floors 1-5 and 7, replacing a boss from the pool for that environment.

The Fallen	The Headless Horseman

Devil and Angel Room

Devil Room

Krampus

Angel Room

Uriel	Gabriel

Seven Deadly Sins and Others

Seven Deadly Sins

The Seven Deadly Sins are mini-bosses that can be encountered on any floor, and will appear on post-Womb/Utero floors as regular enemies. Unlike with regular bosses, there is no special door leading to a mini-boss room, meaning that there is no way to tell whether a room is inhabited by a mini-boss unless the player is in possession of an item that reveals map icons such as Compass or a Map item. Once in a mini-boss room, the player cannot escape through means of bombing the door, as it will be boarded off.

Each of the Sins has specific drops, that are consumables or a pedestal item (less frequently).
In a room containing multiple Sins, only the last one will drop something, allowing you to choose what drop you want by killing a certain mini-boss last.

All them are based on the Seven Deadly Sins.

Envy	Gluttony	Wrath

Pride	Lust	Greed

Sloth

These monsters can also spawn as much stronger alternatives, known as the Seven Super Deadly Sins.

Super Envy	Super Gluttony	Super Wrath

Super Pride	Super Lust	Super Greed

Super Sloth

There is also an Ultra variant of both Pride and Greed. Ultra Pride resembles Edmund and Florian, while Ultra Greed serves as the final boss for Greed Mode.

Ultra Pride

Greed Mode File:DLC Indicator.png

Ultra Greed File:DLC Indicator.png

All Mini-Bosses

The Seven Deadly Sins

Envy	Gluttony	Wrath

Pride	Lust	Greed

Sloth

The Seven Super Deadly Sins

Super Envy	Super Gluttony	Super Wrath

Super Pride	Super Lust	Super Greed

Super Sloth

Ultra Pride

Ultra Pride

Krampus

Krampus

Angels

Uriel	Gabriel

All Bosses

Monstro	Gemini	Larry Jr.

Dingle	Gurglings	Steven

Pin	Widow	Blighted Ovum

Fistula	Gurdy Jr.	The Haunt

The Duke of Flies	Rag Man File:DLC Indicator.png	Little Horn File:DLC Indicator.png

Dangle File:DLC Indicator.png	Turdlings File:DLC Indicator.png	Chub

Gurdy	Mega Maw	C.H.A.D.

Mega Fatty	The Hollow	The Husk

Dark One	Polycephalus	The Frail File:DLC Indicator.png

The Stain File:DLC Indicator.png	The Forsaken File:DLC Indicator.png	Carrion Queen

The Wretched	Peep	The Cage

Monstro II	The Gate	Gish

The Adversary	The Bloat	Mask of Infamy

Loki	Brownie File:DLC Indicator.png	Mr. Fred

Scolex	Mama Gurdy	Lokii

Blastocyst	Daddy Long Legs	Teratoma

Triachnid	The Fallen

The Harbingers

Famine	Pestilence	War
Death	Conquest	The Headless Horseman

Final Bosses

Mom	Mom's Heart	It Lives	Hush File:DLC Indicator.png	Delirium File:Afterbirth† Indicator.png

		File:Boss Isaac (Boss).png
Satan	The Lamb	Isaac	???

Mega Satan	Ultra Greed File:DLC Indicator.png	Ultra Greedier File:Afterbirth† Indicator.png

Trivia

• "Originally every boss/enemy in Isaac was going to resemble Isaac in some way. this is the case for most."[1]
• Double Trouble boss pools can have bosses from any of the previous chapters' pools, and are the same for both versions of that chapter's floor. This means that, for example, Double Trouble boss fights in the Caves can feature bosses from the Cellar or the Basement, and every Double Trouble fight in the Caves can also be encountered in the Catacombs.
• Bosses often come in three versions: normal (For example, Monstro), posthumous (Monstro II), and alternate (Gish). Usually, the posthumous boss looks like the original with some horrible mutilation; for example, Monstro and Chub had most of their skin ripped off.

Bugs

Bug! Defeating a boss quickly enough might cause the boss music to play, even after the boss dies.