The Basement is the first floor of Chapter 1 in The Binding of Isaac, which takes the appearance of an unfinished basement, that possibly has brick walls. The monsters "indigenous" to the chapter are Flies.
Rooms
- 1: The room will always appear once in this floor
- 2: The room will always appear twice in this floor
- Possible: There is a chance for this room to appear, usually due to certain criteria being met
- *: This room can only appear due to a bug or special item
- -: The room cannot appear in this floor
| Rooms with the core game | ||||
| Rooms | Basement 1 | Basement 2 | Basement XL | Note |
|---|---|---|---|---|
| Regular Rooms | 7 - 11 | 13 - 14 | 21-25 | The player must have Wrath of the Lamb installed for The Basement XL to appear. |
 Treasure Room
|
1 | 1 | 2 | |
 Shop
|
1 | 1 | 1 | There is always one shop (except in The Womb / Utero), even in XL floors. |
 Secret Room
|
1 | 1 | 1 | |
 Boss Room
|
1 | 1 | 2 | Boss Rooms are always linked in XL floors. |
 Challenge Room
|
Possible | Possible | Possible | Will only be generated if Isaac has full health while entering the floor. |
 Arcade
|
- | Possible | - | Only generated when Isaac has 5 or more Coins upon entering a new floor or part. |
 Devil Room
|
* | Possible | Possible | *Only reachable by The Joker card. |
| I AM ERROR
|
Possible | Possible | Possible | Only reachable by using the Telepills, which have a 6.66% chance to teleport Isaac to this room. |
| Rooms with Wrath of the Lamb | ||||
| Rooms | Basement 1 | Basement 2 | Basement XL | Note |
| Super Secret Room
|
1 | 1 | 1 | |
 Curse Room
|
Possible | Possible | Possible | |
 Sacrifice Room
|
Possible | Possible | Possible | |
 Angel Room
|
* | Possible | Possible | *Only reachable by The Joker card. |
 Library
|
Possible | Possible | Possible | 5% base chance to spawn, 25% if Isaac is holding a book. |
 Boss Challenge Room
|
* | Possible | Possible | Can spawn on The Basement 1, probably due to a bug. |
Monsters
| Monster | Description | WotL DLC | |
|---|---|---|---|
Black Fly
|
Tiny black flies that do not hurt Isaac upon touch. | ||
Attack Fly
|
Red Flies that follow Isaac and deal touch damage. | ||
Moter
|
Follows Isaac, similar to Attack Flies. Will split into 2 Attack Flies upon death. | ||
Eternal Fly
|
Invulnerable Fly that sticks to corny poop  , Holy Leeches  , Hangmans  , Psychic Maws  , rarely Mr. Maws  and very rarely Maws  .
|
✔ | |
Pooter
|
Moves slowly around, shooting 1 projectile at Isaac when he gets near. | ||
Sucker
|
Flies slowly towards Isaac, exploding into 4 projectiles in a + formation upon death. | ||
Mulligan
|
Harmless enemy that walks around the room, avoiding Isaac. Will spawn multiple flies upon death.
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Mulligoon
|
Harmless enemy that walks around the room, avoiding Isaac. Will drop a Troll Bomb upon death.
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Hopper
|
Jumps around the room slowly, damaging Isaac by touch. | ||
Flaming Hopper
|
Jumps around the room quickly, covering a large distance, similar to Trites.
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Pacer
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Walks aimlessly around the room. Usually spawned after killing a Gaper/Frowning Gaper.
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Gusher
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Walks aimlessly around the room, firing extremely short-ranged blood projectiles from its head. Usually spawned after killing a Gaper/Frowning Gaper.
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| Gaper
|
Walks towards Isaac, dealing contact damage. Usually turns into a Pacer or Gusher upon death.
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Frowning Gaper
|
Walks towards Isaac, dealing contact damage. Usually turns into a Pacer or Gusher upon death.
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Horf
|
Stationary enemy that fires medium ranged blood shots at Isaac. | ||
Clotty
|
Moves around the room, firing 4 blood shots in a plus pattern. | ||
Clot
|
Moves around the room, firing 4 tar shots in an X pattern. | ||
I. Blob
|
Moves around the room, firing 8 shots in all directions. | ✔ | |
| Bosses found in normal rooms: | |||
Embryo
|
Aimlessly hops around the room, damaging Isaac by contact damage. | ||
Bosses
Notes
- Locked treasure rooms cannot spawn on Basement 1 unless it is the XL version of it.
- A Challenge Room cannot spawn on Basement 1. However, Boss Challenge Rooms can.
- A devil room or Angel Room cannot spawn on The Basement 1, but you can teleport there.
- An Arcade cannot spawn on The Basement 1.
- There will be no tutorial if you spawned in a XL floor.
Room-layouts
The very first room in the Basement
Spawn Room within The Basement 1.
A room with absolutely nothing within it.
A lone Black Fly, notably the least threatening room in the game to ever spawn an enemy.
Three Attack Flies in the center.
A lone Moter in the center of the room.
A room with a single Gusher.
A single Horf within the center.
A lone Frowning Gaper.
Two Gapers in the center of the room.
Four Hoppers, one in each corner of the room.
A single chest in the center of the room.
A single pile of poop in the center.
Two piles of poop on either side of the center.
Three Mulligans scattered throughout three piles of poop and a rock in the top-right corner.
A room full of eight Pacers.
Two Mulligoons and a Hopper in the center of the room, with a rock at opposing corners.
Two Frowning Gapers close together in the center of the room, with a rock at opposing corners and two piles of poop in the other two corners.
Two Attack Flies in the center, with a rock in each corner of the room.
Two Moters in a room with three piles of poop.
A lone Sucker in the center of three rocks, with an additional rock and pile of poop at opposing corners.
Five Flies, consisting of 1 Attack Fly and 4 Black Flies, scattered among 4 piles of poop.
A single Pooter in a room scattered with piles of poop and rocks.
Two Frowning Gapers in the center of a room with rocks at opposing corners.
A Bomb in the center between two rocks and a fire on each side of the room.
Five attack flies between two columns of poop.
Four coins surrounding a lone rock in the center of the room.
Two Hoppers with three asymmetric rocks in the center.
A Key in the top-left corner with a golden chest in the bottom-right corner, each blocked off by a pair of rocks. Two additional rocks at the other opposing corners.
Four Attack Flies surrounding a plus of rocks in the center, with additional rocks and poop in the corners of the room.
An identical coin room from before, only with two additional rocks at the top-right and bottom-left of the center.
A lone Horf in the center of four rocks, with a pile of poop at opposing corners.
Two embryoes of Blastocyst on either side of the four rocks in the center of the room.
Four embryo Blastocysts at each corner of the four rocks in the center of the room, all surrounding a single pile of poop.
Three Attack Flies and two Pooters with a rock on each wall of the room.
A lone Clotty, with two rocks at each corner.
Two Frowning Gapers between two rows of rocks, with a pile of poop at each corner of the room.
A Horf stuck between two piles of poop and two rocks, surrounded by three Black Flies and columns of three rocks at opposing corners of the room.
Two Hoppers, each hugging a wall with columns of rocks and a pile of poop at opposite corners.
Two Horfs, each trapped in two columns of rocks that are sealed with a pile of poop.
A Horf with four Attack Flies between two columns of rocks, with additional rocks in each corner of the room.
A diamond of rocks with a pile of poop on the left, surrounding a random item. Four spots of Fire take the corners of the room.
Two Hearts in what appears to be a skull pattern of rocks.
A square of rocks blocking off a Chest.
Two Attack Flies in the middle of a square of rocks, with a Gusher at opposing corners of the room.
Four Frowning Gapers surround a rock in the center of the room, of which are surrounded by six rocks.
Five Gapers formed in a cross between two rows of rocks.
A quadret of Gapers within a circle of rocks.
Four Frowning Gapers enclosed by rocks and piles of poop.
Four Frowning Gapers scattered within a ring of rocks.
Four Frowning Gapers horizontally aligned in a ring of rocks.
A multitude of rocks encasing three Coins, with an additional rock at each corner of the room.
Three Hoppers within a large mass of rocks. There is an additional gap in the bottom-right part of the rocks, yet monsters will never spawn in it.
Four Black Flies surrounding a Pooter in the center. Five rocks in a skinny X pattern appear on both sides of the room.
Three Frowning Gapers aligned in the middle of a room scattered with rocks.
Two Gapers in a room filled with narrow pathways of rocks.
Two Pooters and four Black Flies scattered throughout a room filled with narrow pathways of rocks.
Three Black Flies with a Pooter at opposing corners of the room. A pair of rocks appear at the other opposing corners, with one of them enclosing a chest.
Three Hoppers, each next to an assortment of rocks, with two piles of poop in opposing corners of the room.
A diagonally symmetrical room with a Clotty in the center and a Black Fly at each corner. There are many rocks and three piles of poop at opposing corners.
Two Horfs in the center of the room, with many rocks acting as cover.
Two Mulligans and two Attack Flies surrounded by many rocks.
Two Mulligans in the center of the room, with Frowning Gapers forced to walk a pathway walled by rocks at opposing corners of the room.
Two Horfs at opposing corners of the room, located between rocks.
Four Horfs between various rocks, as well as two Attack Flies at opposing corners of the room.
A Horf and two Pooters scattered about six rocks in the middle of the room.
Four Black Flies and three rocks at each corner of the room, with an additional Attack Fly at the top-left corner and a pile of poop in the center.
A room full of flies, consisting of three Attack Flies, five Black Flies, and two Pooters. There are eight pairs of rocks as well.
A Horf in the center, with an Attack Fly in the middle of a row of rocks and piles of poop at each corner of the room.
A room with ten coins, 2-3 in each corner, walled off by rocks.
Two Attack Flies in opposing corners, with a Hopper and two coins in each of the other corners, every corner being sealed off by rocks.
Attack Flies behind a pair of rocks, each in their own corner, with an open circle of rocks in the center.
Multiple rock cages, with a golden chest in the center and two Hoppers in opposing corners.
Four Gusher in a rock oval opened to all four sides and sealed with poop. On the top and the bottom, left and right of the middle Poop are four Gaper.
An oval of rocks concealing four Attack Flies and two rows of poop.
A Gaper and two Gushers in the center of the room, between two columns of rocks and an additional rock and pile of poop at opposing corners.
Two Frowning Gapers in the center of a room with four piles of poop encased in a wall of rock in each corner of the room.
Two Frowning Gapers in the 'C' formations of rocks, with a Pooter in the center of the room.
Five rocks in each corner of the room, two corners holding Hoppers while the other two hold bombs.
Three Horfs in the dips of a zig-zag formation of rocks.
Three Horfs in three corners of the room. A chest lies in the middle of a formation of rocks shaped like a triangle pointed left.
Two Horfs, each in a chokepoint of rocks at opposing corners of the room.
Fortune Telling Machine in center, bordered by two fires.
Two lines of Poop.
A cross of fire.
Fireplace formation resembling a reversed pentagram or a devil's head.
Gluttony's arena, notably the only instance where holes are found in The Basement.
Sloth's arena.
Wrath's arena.
Monstro's arena.
Before, only with two Black Flies as well.
Monstro's arena with a pile of poop at each corner.
Larry Jr.'s arena.
Same as before, with no corner rocks.
Arena variant with two rows of poop instead of rocks.
Variant of Larry Jr. with Rocks in a 'H'-Shape
Another variant of Larry Jr's arena, this time with no rocks.
The Duke of Flies' arena.
The Duke of Flies' arena variant.
Gemini's arena.
Famine's arena.
Steven's arena.
The Headless Horseman's arena.
2 Larry Jr's being stuck.
3 Larry Jr.'s in the Basement Boss room.
A single seven-segmented Larry encountered in Basement 2.
A soul heart and a regular heart obtained using the infinite poop generation method sitting on top of each other.
One of the Mulligoons about to explode.
Battling Pride.
Battling Super Pride.
Two champion Gapers in a room, the right one dropped a key and the right one dropped a coin.
Multiple Champion Frowning Gapers.
A normal elder Gemini with a blue champion version of the baby.
Related Achievements
The Radioactive Spider - Complete The Basement once.
Monstro's Tooth - Defeat all of the bosses in The Basement. (Duke of Flies, Monstro, Gemini, Larry Jr.)
Basement Boy - Complete The Basement without taking damage.
| Chapters | |||||
|---|---|---|---|---|---|
| Chapter 1 | Chapter 2 | Chapter 3 | Chapter 4 | Chapter 5 | Chapter 6 |
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