Bosses are enemies in The Binding of Isaac: Rebirth that play a major role in the game's mechanics.
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.
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.
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.
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.
Below is a list of all Bosses found within The Binding of Isaac.
|The Forsaken||Hush||Little Horn|
|Rag Man||The Stain||Turdlings|