Bosses are enemies in The Binding of Isaac: Rebirth that play a major role in the game's mechanics.

Upon Dying

Bosses generally have relatively high health compared to that of Monsters and drop a Passive Collectible upon dying, this Passive Collectible generally being either a Damage Up or an HP Up. Bosses also drop Red Hearts on death, with few exceptions (some Champion Bosses dropping one Soul Heart). The chance of Bosses dropping Red Hearts on death are greatly reduced on Hardmode. After killing a Boss in a Boss Room, the door will open and a trapdoor to the next floor will spawn. Also after killing a Boss in a Boss Room, a Devil or Angel Room has a chance to spawn.

Rooms of Appearance

Bosses can appear in a variety of Rooms in different forms.

Boss Rooms

Every Boss can be found in a Room called a Boss Room (with the exception of Mega Satan, Krampus, and The Angels), in which Isaac must engage in a Boss Fight to advance to the next Floor, with few exceptions around this, one of these exceptions being the We Need To Dig Deeper Item. Boss Rooms cannot be exited once entered unless either the Boss is defeated or Isaac is teleported to a different Room, with few exceptions, one exception being if the player uses Dad's Key. When Bosses spawn in Boss Rooms, they can occasionally spawn alongside one or two Monsters.

Boss Challenge Rooms

Most Bosses can also be found as Monsters in Boss Challenge Rooms, Rooms that can only be entered when Isaac has 1 Red Heart Container or less. Boss Challenge Rooms generally have Chests or Item Pedestals in the middle of them. When Isaac either opens one of these Chests or takes an Item, they will engage in a battle with 2-3 waves of Bosses. These Bosses are considered Monsters, for they do not drop Passive Collectibles upon dying. Said Bosses also do not drop many Red Hearts on death.

Later Floors

Most Bosses can be found as Monsters on later Floors in the game. They are generally in pairs, especially in advanced Floors such as The Chest and The Darkroom. They do not drop Passive Collectibles or many Red Hearts on death. Some Bosses' difficulties have been toned down a bit as Monsters, an example being Gurglings.

Boss Rush

All Bosses that were not introduced in Rebirth can be found during Boss Rush, with the exception of Isaac (Boss), Blue Baby (Boss), Mom, Satan, Scolex, and Krampus. Boss Rush is located in a secret room that is only accessible after defeating Mom in under 20 minutes. Upon first entering the room, four Item Pedestals will be seated in the middle of the Room. If Isaac chooses to take an Item, the rest of the Items will disappear and Boss Rush will begin. Isaac will be forced to fight through 15 waves of Bosses (that is, if they don't teleport, use We Need To Dig Deeper, etc.), each wave containing two Bosses. None of these Bosses drop Collectibles, but they still drop Hearts. Once again, this chance is greatly reduced to what seems to be around a 0% chance to drop Red Hearts during Hard Mode. Also during Hard Mode, most Bosses will spawn as Champion Bosses. At the end of Boss Rush, one more Item Pedestal will spawn and the player is allowed to leave the Room.

Boss List

Below is a list of all Bosses found within The Binding of Isaac.

Adversary Portrait Blastocyst Portrait The Blighted Ovum Portrait
The Adversary Blastocyst Blighted Ovum
Blue Baby (Boss) Portrait The Cage Portrait Carrion Queen Portrait
Blue Baby (Boss) The Cage The Carrion Queen
Chad Portrait Chub Portrait Conquest Portrait
C.H.A.D. Chub Conquest
Daddy Long Legs Portrait Dark One Portrait Death Portrait
Daddy Long Legs Dark One Death
Dingle Portrait Duke of Flies Portrait The Fallen Portrait
Dingle The Duke of Flies The Fallen
Famine Portrait Fistula Portrait The Gate Portrait
Famine Fistula The Gate
Gemini Portrait Gish Portrait Gurdy Jr Portrait
Gemini Gish Gurdy Jr.
Gurdy Portrait Gurglings Portrait The Haunt Portrait
Gurdy Gurglings The Haunt
Headless Horseman Portrait The Hollow Portrait The Husk Portrait
Headless Horseman The Hollow The Husk
Isaac Portrait It Lives Portrait The Lamb Portrait
Isaac (Boss) It Lives The Lamb
Larry Jr Portrait Loki Portrait Lokii Portrait
Larry Jr. Loki Lokii
Mask of Infamy Portrait Mega Gurdy Portrait Mega Fatty Portrait
Mask of Infamy Mama Gurdy Mega Fatty
Mega Fred Portrait Mega Maw Portrait Mega Satan Portrait
Mega Fred Mega Maw Mega Satan
Mom Portrait Mom's Heart Portrait Monstro Portrait
Mom (Boss) Mom's Heart Monstro
Monstro II Portrait Peep Portrait Pestilence Portrait
Monstro II Peep Pestilence
Pin Portrait Polycephalus Portrait Satan Portrait
Pin Polycephalus Satan
Scolex Portrait Steven Portrait Teratoma Portrait
Scolex Steven (Boss) Teratoma
Triachnid Portrait The Widow Portrait The Wretched Portrait
Triachnid Widow The Wretched
Brownie Portrait Dangle Portrait The Frail Portrait
Brownie Dangle The Frail
The Forsaken Portrait Hush Portrait Little Horn Portrait
The Forsaken Hush Little Horn
Rag Man Portrait The Stain Portrait Turdlings Portrait
Rag Man The Stain Turdlings
Ultra Greed Portrait
Ultra Greed
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