The Binding of Isaac is the result of putting The Legend of Zelda, Smash TV, a roguelike, and a couple of dead baby jokes into a blender...and hitting Liquefy.

An expansion pack, Wrath of the Lamb, added more enemies, more levels, more items, more dungeon features, more bosses, more unused content, and more bugs. A little later after that came another expansion pack, 'Eternal Edition', that added some more stuff.

Three years after release, a remake of the game was released, titled The Binding of Isaac: Rebirth.

Unused Sounds

Powerup_Zelda_Headlift

A sound that probably would've been used for getting an item similar to The Legend of Zelda (Hence the file name).

Unused Room Layouts

When Wrath of the Lamb was released, a lot of room layouts were added; in fact, a handful of rooms were added that are never able to be seen in-game! These rooms exist only in the flash assets and their ID values are never generated in-game, but Cheat Engine can be used to reveal them. They are all fully functional; they were either purposefully left out or (most likely) omitted due to an oversight during room generation.

Basement/Cellar

Unused Basement rooms: B1 , B2

, Unused Cellar rooms: B2

Basement Room B1

Basement Room B2

Cellar Room B2

Caves/Catacombs

Unused Caves rooms: A9 , AA

, Unused Catacombs rooms: AA

Caves Room A9

Caves Room AA

Catacombs Room AA

The Depths/Necropolis

Unused Depths rooms: 9A , 9B

, Unused Necropolis rooms: 9B

Depths Room 9A

Depths Room 9B

Necropolis Room 9B

The Womb/Utero

Unused Womb rooms: 89

Unused Utero rooms: 89

Womb Room 89

Utero Room 89

Sheol/Cathedral

Surprisingly, there are 11 unused rooms for Sheol; however, all of these rooms save for one have an equivalent in the Cathedral that is used in-game. Some of them also appear to be similar to already existing Sheol rooms.

Unused Sheol rooms: 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 5A , 5B , 5C

, , , , , , , , , , Unused Cathedral rooms: 5C

Sheol Room 52

Sheol Room 53

Sheol Room 54

Sheol Room 55

Sheol Room 56

Sheol Room 57

Sheol Room 58

Sheol Room 59

Sheol Room 5A

Sheol Room 5B

Sheol Room 5C

Cathedral Room 5C

The Chest

Unused Chest rooms: 06 , 07

Chest Room 06

Chest Room 07

Unused Items

Pumpkin Mask

The Pumpkin Mask is an Activated Item that was intended to be dropped by Krampus. It was supposed to shoot a beam in four directions. It was replaced with A Lump of Coal before the halloween update released. A similar item is obtainable in Rebirth, Krampus's Head. You are able to view the sprite by finding an undefined item, or hacking the item itself in. Its properties have been replaced with A Lump of Coal's.