In The Binding of Isaac, every object or room that has a chance of spawning an item (Boss Rooms, Golden Chests, etc.) has a specific item pool from which it draws, ensuring that the item obtained is appropriate.
Mechanics[]
When an item is to be created, it is selected from the corresponding pool. For example, a Secret Room will draw from the Secret Room Pool when it contains an item or an item is rerolled inside of it. Whenever an item is picked up, it is removed from the pool that spawned it; seeing the item will result in one copy of the item being removed. Depleting the Boss Pool will force the use of the Secret Room Pool; depleting all others forces the use of the normal Treasure Room Pool instead. Depleting the Treasure Room Pool to 5 items or less will cause it to be refreshed. In certain cases, however, the game will crash; this is because with items that are in both the Treasure Room Pool and another pool, picking that item up in the other pool, (e.g. My Little Unicorn in the Secret Room) will not remove it from the Treasure Room Pool, but will instead make it so that that item cannot appear in the Treasure Room Pool; therefore, touching more than 5 items that are in the Treasure Room and another pool in the other pool will prevent the Treasure Room Pool from being able to refresh and mean that the game will crash when it runs out of items.
Unique Item Pool Modification[]
In order to decrease redundancy, certain items can be removed from pools even if they are not picked up. In the list below, the first event prevents the player from obtaining the item that follows.
- Using a Health Up / Down pill: <3
- Using a Speed Up / Down pill: Wooden Spoon
- Using a Tears Up / Down pill: Wire Coat Hanger!
- Using a Range Up / Down pill: Mom's Lipstick
- Finishing an Eternal Heart / Making a deal with Satan: Lunch
- Obtaining Dead Cat: Dinner
- Obtaining Sacred Heart: Spoon Bender
- Obtaining Ipecac / Polyphemus / Mutant Spider: The Inner Eye
- Obtaining Spirit of the Night / Dead Dove: Ouija Board
- Obtaining Pretty Fly by using a Slot Machine or through a pill: Halo of Flies
Additionally, obtaining the Rosary will add seven copies of The Bible to the Shop Pool, and obtaining Dr. Fetus will add six copies of Mr. Mega and Bobby-Bomb to the Treasure Room pool.
Treasure Room Pool[]
- The Sad Onion
- The Inner Eye
- Spoon Bender
- Max's Head
- My Reflection
- Number One
- Blood Of The Martyr
- Brother Bobby (x2)
- Halo Of Flies
- Magic Mushroom
- The Virus
- Roid Rage
- <3
- Boom! (x2)
- Wooden Spoon
- The Belt
- Mom's Underwear
- Mom's Heels
- Mom's Lipstick
- Mr. Boom
- Tammy's Head
- Mom's Bra
- Kamikaze!
- Mom's Pad
- Teleport!
- Doctor's Remote
- Cupid's Arrow
- Shoop Da Whoop!
- Magneto
- Mom's Eye
- Lemon Mishap
- Distant Admiration
- Book of Shadows
- Wiggle Worm
- Charm Of The Vampire
- Anarchist Cookbook
- The Hourglass
- Sister Maggy
- Chocolate Milk
- Growth Hormones
- Mini Mushroom
- Rosary
- PHD
- XRay Vision
- My Little Unicorn
- Deck of Cards
- Ouija Board
- Odd Mushroom (Large)
- Odd Mushroom (Thin)
- Dead Sea Scrolls
- Bobby-Bomb
- Forever Alone
- Bucket of Lard
- Best Friend
- Remote Detonator
- Stigmata
- Bob's Curse
- Scapular
- Speed Ball
- Bum Friend
- Infestation
- Ipecac
- Tough Love
- The Mulligan
- Technology 2
- Mutant Spider
- Chemical Peel
- The Peeper
- Bloody Lust
- Crack the Sky
- Ghost Baby
- Harlequin Baby
- Polyphemus
- Mitre
- Portable Slot
- Holy Water
- The Black Bean
- Toothpicks
- 3 Dollar Bill
- Telepathy for Dummies
- D20
- Celtic Cross
- Abel
- Sacrificial Dagger
- Rainbow Baby
- Blood Rights
- SMB Super Fan!
- Spider Butt
- Daddy Longlegs
- Guppy's Hair Ball
- Skeleton Key (1/2 chance)
- The Necronomicon (2/3 chance)
- Technology (4/5 chance)
- The Book Of Belial (1/3 chance and not Judas)
- Yum Heart
- Lucky Foot (2/3 chance)
- A Quarter (2/3 chance)
- Dr. Fetus
- The Poop
- Spelunker Hat
- Monstro's Tooth
- Loki's Horns
- Little Chubby
- The Relic
- Sack Of Pennies
- Robo-Baby
- The Gamekid
- The Book Of Sin (2/3 chance)
- Little Gish
- Little Steve
- Little C.H.A.D.
- The Halo
- Mom's Bottle of Pills
- The Common Cold (2/3 chance)
- The Parasite (2/3 chance)
- The Dice
- Mr. Mega
- The Pinking Shears
- The Wafer
- Money = Power (2/3 chance)
- Mom's Contacts
- The Bean
- Dead Bird
- Guardian Angel
- Bomb Bag
- Mom's Knife (2/3 chance)
- Whore of Babylon (2/3 chance)
- Razor Blade (2/3 chance)
- Demon Baby (2/3 chance)
- Forget Me Now (2/3 chance)
- Monster Manuel (2/3 chance)
Boss Room Pool[]
- Lunch
- Dinner
- Dessert
- Breakfast
- Rotten Meat
- One of:
- Two (possibly the same item) of:
- Wire Coat Hanger!
- Pentagram
- Pageant Boy
- Cat-O-Nine-Tails
- Stem Cells
- MEAT!
- Magic 8 Ball
- Mom's Coin Purse
- Squeezy
- Jesus Juice
- Box
- Super Bandage (2/3 chance)
The first occurrence of every item in this pool is removed from the Treasure Room Pool.
Secret Room Pool[]
- 1UP (1/2 chance for x2)
- Raw Liver
- Bob's Rotten Head
- My Little Unicorn (1/2 chance for x2)
- Ankh
- Pyro (1/2 chance)
- Dad's Key
- Epic Fetus
- We Need To Go Deeper! (1/2 chance)
- The Book Of Belial (1/2 chance)
- Transcendence (2/3 chance)
- Spider's Bite
Shop Pool[]
- Treasure Map (x2)
- The Ladder (x2)
- Steam Sale
- The Compass (x2)
- Mom's Purse
- Habit
- Notched Axe
- Mom's Coin Purse
- Bum Friend (1/2 chance)
- Portable Slot (if not Bum Friend)
- The Candle
- 9 Volt (1/2 chance)
- The Battery (1/2 chance)
- Book Of Revelations
The first occurrence of every item in this pool is removed from the Treasure Room Pool.
Golden Chest Pool[]
- Tammy's Head
- Rotten Meat
- The Sad Onion
- Steven
- Monstro's Tooth
- Fate (1/2 chance)
- One of:
- One of:
The first occurrence of every item in this pool is removed from the Treasure Room Pool.
When in The Chest, all chests spawn items from the Treasure Room Pool.
Devil Room Pool[]
- Brother Bobby
- Sister Maggy
- The Mark
- The Pact
- Dead Cat
- Ouija Board
- Brimstone
- Guppy's Paw
- Guppy's Head
- Guppy's Tail
- Spirit Of The Night
- Bloody Lust
- Whore Of Babylon
- Mom's Knife
- The Necronomicon (2/9 chance)
- Technology (1/5 chance)
- Lord Of The Pit (1/3 chance)
- We Need To Go Deeper! (1/3 chance)
- The Book Of Belial (1/6 chance)
- Lucky Foot (1/3 chance)
- The Nail (2/3 chance)
- A Quarter (1/3 chance)
- The Book Of Sin (1/3)
- The Common Cold (1/3 chance)
- The Parasite (1/3 chance)
- Money=Power (1/3 chance)
- Razor Blade (1/3 chance)
- Demon Baby (1/3 chance)
- Forget Me Now (1/3 chance)
- Monster Manuel (1/3 chance)
Challenge Room Pool[]
Library Pool[]
- How to Jump
- The Bible
- Book Of Shadows
- Anarchist Cookbook
- Telepathy For Dummies
- The Necronomicon (2/3 chance)
- The Book Of Belial (if not Judas)
- Book Of Revelations
- The Book Of Sin
- Monster Manuel
Because the library has such a small pool, and it removes two items at a time, this allows for an exploit with the Dice.
Angel Room Pool[]
- Blood Of The Martyr
- The Bible
- The Halo
- Prayer Card
- Scapular
- Mitre
- Sacred Heart
- Holy Grail (1/2 chance for x2)
- Dead Dove
- The Relic
- Guardian Angel
Items cannot be removed from this pool.