dpatti/mechanics.md

## mechanics.md

      
    Raw
  

              mechanics.md
            
          
    Binding of Isaac Mechanics Guide

Stats

Health

Each character starts with the following health

Isaac: 3
Maggy: 4
Cain:  2
Judas: 1
???:   3
Eve:   2
Sam:   1

Additional heart containers can be obtained via the following items:
+1 max heart


Lunch
Dinner
Dessert
Breakfast
Rotten Meat
Magic Mushroom
Odd Mushroom (Large)
The Halo
<3
Stem Cells
Holy Grail
MEAT!
SMB Super Fan!
Stigmata
Blood Bag

+2 max hearts


Raw Liver
Bucket of Lard

Luck

Luck is a bit of a mystery stat.

Luck starts at 0
If you're doing the "7 Years Bad Luck" challenge, you start with -2 luck
You can increase/decrease your luck by 1 with a "Luck Up/Down" pill
If you have Tough Love, a tooth will fire off with a probability of 1/(10 - luck). This means that a luck of 10 will guarantee a tooth, while a base luck
of 0 gives you a tooth with 1/10 chance. I am not sure what will happen with
more than 10 luck (random(-1) in ActionScript 2)
Luck affects the chance that you get an item after a room (see "Clearing a
Room" section)

Movement Speed (_root.playsp)


Base speed: 1
Modifiers (upper bound 1):

Blood Bag: 0.3
Wooden Spoon: 0.3
Belt: 0.3
Mini Mush: 0.3
Halo: 0.3
Whore of Babylon: 0.3
Odd Mushroom (Small): 0.3
Roid Rage: 0.6 (upper bounded at 1)
The Virus: -0.1 (lower bounded at -1 with Odd Mushroom (Large))
Odd Mushroom (Large): -0.1
Character bonus

Isaac: 0
Maggy: -0.15
Cain:  0.3
Judas: 0
???:   0.1
Eve:   0.23
Sam:   0.1


Growth hormones: 0.4
The Mark: 0.2
Lord of the Pit: 0.3


Small Rock: -0.2
Bucket of Lard: -0.2
SMB Super Fan: -0.2
Chariot card, My Little Unicon, The Gamekid activated: 0.28
Goat Hoof: 0.15
The Nail activated: 0.18
Holding A Pony or White Pony: speed lower bounded at 1.5

Projectile Speed (create(): f7 == 2)


Base: 1
Modifiers (upper bound 0.4):

Speed Ball: +0.2
Cat-o-nine-tails: +0.23
Stem Cells: +0.16
Tooth Picks: +0.16
Magic 8: +0.16
Sacred Heart: -0.25
Samson: +0.31


Fire Rate (firr())


Rate modifiers

Number One: 1.5
Wire Coat: 0.7
Pact: 0.7
Sad Onion: 0.7
Odd Mushroom (Small): 1.7
Squeezy: 0.4
Wiggle: 0.4
Sacred Heart: -0.4
Halo: 0.2
Small Rock: 0.2
SMB Super Fan!: 0.2
Samson: -0.25


Calculation:
  base = 16
  If positive modifiers:
    delay = 16 - sqrt(1 + modifiers * 1.3) * 6
  If negative modifiers:
    delay = 16 - modifiers * 6 (double negative means higher delay)


Post-calculation Multipliers

Chocolate Milk: delay = delay * 0.8
Inner Eye, Ipecac, Polyphemus, or Mutant Spider: delay = delay * 2.1 + 3
Cancer: delay = delay - 2


Damage (dmgdo())

Damage Sources


Devil Card or Book of Belial: 2
Blood of the Martyr: 1
Small Rock: 1
Money=Power: coins * 0.04
Whore of Babylon: 1.5 * val^2

val = 1.5 if triggered via Empress Card
val = 1.2 if triggered by falling below 1 heart
val = 1.0 if triggered in a different room and has not left


Steven: 1
Pentagram: 1
Growth Hormones: 1
The Mark: 1
The Pact: 0.5
Max's Head: 0.5
Jesus Juice: 0.5
Magic Mushroom: 0.3
The Halo: 0.3
Odd Mushroom (large): 0.3
Stigmata: 0.3
MEAT!: 0.3
SMB Super Fan!: 0.3
The Nail (used): 0.7
Rage Effect (+1 damage per point)

Starts at +0
Bloody Lust

When you kill a creature, you get +0.28 up to a cap of 3.3


Samson's Lock

When you kill a creature, you get +0.50 up to a cap of 3.3


Razor Effect (+0.6 damage per point, applied after Odd Mushroom (small) below)

Starts at +0
Red Patch

When you take damage, 1/5 chance to get +3 razor


Razor Blade (use)

When you use razor blade, add +2 razor


Other Interactions


Chemical Peel +2 damage if:

Every other tear
As Cain, 50% chance


Odd Mushroom (small): damage = damage * 0.9 - 0.4
Chocolate Milk without Brimstone

Charge power starts at 1
Gain 1/10 charge power every frame (equates to 3 charge power per second)
Charge power caps at 5 (4/3 seconds charge length)
Damage bonus = (Charge power * 1.8 - 3) * 1.3
Damage bonus cannot go below 0
Full charge equivalent to +7.8 damage


Main Calculations


Sum all the above effects
damage = 3.5 * sqrt(1 + damage * 1.2)
If polyphemus:

If inner eye or mutant spider:

damage += 5


Else

damage = 2 * (damage + 4)


damage = character_mod * damage

Isaac: 1.00
Maggy: 1.00
Cain:  1.20
Judas: 1.35
???:   1.05
Eve:   0.75
Sam:   1.00


More damage applications

Curved Horn: damage = damage + 2
Sacred Heart:  damage = damage * 2.3 + 1
Technology 2: damage = damage * 0.65
Tears only:

Tough love: 1/(10 - luck) chance: damage = damage * 3.2
Lump of Coal: +0.14 damage every frame up to a maximum of 150 frames (5
seconds) for a maximum total of +21 damage
damage = damage * 1.5 if at least one of the following three:

Max's Head
The Devil Card/Book of Belial with Blood of the Martyr
Magic Mushroom


Damage benchmarks

To express the amount of basic +damage items you need using the above values to
increase your damage:

x2 damage: 2.5
x3 damage: 6.67
x4 damage: 12.5
x5 damage: 20.0

Non-basic damage


Lasers

Technology, Brimstone

If you have Ipecac, The Inner Eye, Mutant Spider, or Polyphemus: damage = damage * 3
If you have A Lump of Coal: damage = damage + 2
If Brimstone, damage = damage * 3

If also Chocolate Milk, damage scales linearly to 100% at 60
frames (2 seconds) of charge


Technology 2

Damage every 3 frames (10 times per second)
Damage = damage * ?secol * 0.2

Every time you fire a tear, ?secol = ?secol + 1
Every time the lazer does damage, ?secol = ?secol * 0.8 + 0.2


Mom's Knife

Base: damage * (2 + ?knill)
?knill is bounded to the range [0,4]
This is the most confusing clusterfuck of variable manipulation I have
ever seen. I have no idea what is going on.


Blue Flies

Each fly does 2x base damage (before tear calculations)
A blue fly will spawn with a projectile or laser hit if one of the
following is true:

Non-familiar projectile and 1/6 chance
Transformed into Guppy, queued blue flies < 1, objects < 30, and 1/3 chance if you have Technology 2

Queued blue flies is drained by one every frame, so this mostly
prevents things like Mutant Spider from granting 4 flies per shot
Objects refers to pretty much anything on the screen - pickups,
enemies, projectiles, and possibly rocks.


The way this was written is likely buggy, as this means that familiars can
spawn flies if you are Guppy, and extra blue flies can spawn (i.e., from
Mutant Spider) with 1/6 chance after the first.


Red Tears

Though cosmetic, the tear color changes to red under the following conditions

You do not have Ipecac
You have one of the following items:

SMB Super Fan!
Blood of the Martyr
Tooth Picks


You have a Devil Card, Book of Belial, Whore of Babylon, or The Nail activated
Your final damage is over 5.5 (without Polyphemus)
Your final damage is over 15 (with Polyphemus)
If you have Chocolate Milk, the damage conditions above are not applicable
You are shooting from your empty eye socket with Peeper

Item Mechanics

Items that give drops


Magic 8 ball: ?kogs = [5.3]
Mom's Coin Purse: ?kogs = [5.07, 5.07, 5.07, 5.07]
Squeezy: kogs = [5.010000003, 5.010000003]
BOX: kogs = [5.35, 5.07, 5.02, 5.010000003, 5.3, 5.03, 5.04]

Temporary Effects


?ceye: Compass
?world: Treasure Map + Compass
3 dollar bill: Random tear
Whore of Babylon: on if player hearts < 1
Liberty Cap + 1/4 chance:

Compass
Mini Mush
Odd Mushroom (small)
Odd Mushroom (large)


Cancelled Effects


Dr. Fetus cancels...

Chocolate Milk


Epic Fetus cancels...

Chocolate Milk
Brimstone
Mom's Knife


Mom's Knife cancels...

Brimstone


Health Restoration

+0.5 hearts

Bucket of Lard

+1 heart

Lunch
Dinner
Dessert
Breakfast
Rotten Meat
MEAT!
Stigmata
SMB Super Fan!
The Halo
Super Bandage
Fate (if you complete an eternal heart)

+1.5 hearts

Stem cells

+2 hearts

PHD

+5 hearts

Blood bag

Full restoration

Sacred Heart
Magic Mushroom
<3
Raw Liver

Spirit Hearts

From item pickups

Super Bandage: 2
Sacred Heart: 1
Rosary: 3
The Mark: 1
The Pact: 2

Eternal Hearts


Fate: 1/2 heart

Gives Stuff


Bombs

Pyro: 99
Remote Detonator: 5 (first time only)
Bobs Curse: 5
Bobby - Bomb: 5
Mr. Mega: 5
Boom!: 10


Keys

Skeleton Key: 99


Coins

A dollar!: 99
A Quarter: 25


Familiars


Projectile: All 3.5(?)

Brother bobby
Sister Maggy
The Robo-Baby
Little Gish
Little Steve
Demon Baby
Ghost Baby
Harlequin Baby
Rainbow Baby
Abel
Isaac's Head


Other combat

Mom's Knife
Cube of Meat: 7
Meatboy: 3.5
Full Meatboy: 5.5
Guardian Angel: 7
The Peeper: 8
Guppy's Hairball: 3 + size * 2
Sacrificial Dagger: 15
Dead Bird: 2
Daddy Longlegs: 20
The Pinking Shears: 7
Halo of Flies: 2
Distant Admiration: 5
Forever Alone: 2
Lil Chubby: ?killshit()
Blue Flies: 2 * damage


Non-combat

Bum Friend
Dead Cat
1up!
Sack of Pennies
Little Chad
The Relic
Bomb Bag
Holy Water
???'s Soul


Pills


PHD has a 1/150 chance of identifying a pill every frame (30 times/s).
If you find a negative pill and then acquire PHD or Lucky Foot, it will become
its positive counter-part (Full Health being Bad Trip's).
Range Down pills will become Range Up if you have Number One and ?chaps < 8.
When using or identifying a pill, the following sequence is executed, stopping
whenever the pill has been decided. If another pill has this same effect, then
the process starts over.

If you have less than max hearts (or are playing ??? and have less than 3 spirit
hearts), 1/10 chance to get Full Health
1/13 chance to get Bad Gas
1/17 chance to get Friends til the end!
1/17 chance to get Luck Up/Down
If you don't have PHD, 1/15 chance to get I Found Pills
1/10 chance to get Explosive Diarrhea (always fails by bug in code)
1/10 chance to get Balls of Steel
1/20 chance to get Pretty Fly
If current hearts + spirit hearts > 1 and you don't have PHD or Lucky Foot, 1/9
chance to get Bad Trip!
1/7 chance to get Health Up/Down
If either bombs or keys are over 0, 1/6 chance to get Bombs are Key
1/5 chance or 1/4 chance to get Tears Up/Down (equivalent to 4/10
chance)
1/3 chance to get Range Up/Down
1/3 chance to get Speed Up/Down (guaranteed if you have PHD)
If nothing else, Telepills (obviously impossible with PHD)


All above Up/Down pills have an equal chance of spawning the Up or Down
version
Pills effects

Tears Up: Adds Wire Coat hanger! +0.5
Tears Down: Adds Wire Coat hanger! -0.4
Range Up: Adds Moms Lipstick +0.5
Range Down: Adds Moms Lipstick -0.4
Speed Up: Adds Wooden Spoon +1
Speed Down: Adds Wooden Spoon -0.8


Cards tater()


4/5 chance to get random Tarot Card (22 total)
Otherwise random Deck Card (5 total)
Card effects

Strength: Magic Mushroom
Death: 60 damage to all enemies
The Devil: Book of Belial use effect


Trinkets

Trinket Pool


?poli -> Guaranteed Polaroid
Counterfeit Penny is not in the pool, but has a 1/3 chance to spawn from
golden poop
Else -> Random trinket removed from the pool immediately
No trinkets left? Random card as above

Fish Head

Every time you get hit, you spawn one blue fly
Pinky Eye


1/10 chance to make a poison tear
If you have Technology, has a 1/10 chance of temporaraily disabling The common
cold if you have it (possibly just for the color change)

Push Pin

1/10 chance to make a spectral tear
Liberty Cap

1/4 chance to give one of the following effects:
* Compass
* Mini Mush
* Odd Mushroom (small)
* Odd Mushroom (large)
Umbilical Cord

If you take damage have less than 1/2 heart (including spirit hearts), you gain
Little Steve for the remainder of the room.
Pickup-boosting trinkets


1/10 chance to give you an item at the end of a room
2/3 chance to give you an item when opening a chest
Types

Child's Heart: Heart
Rusted Key: Key
Match Stick: Bomb
Safety Cap: Pill
Ace of Spades: Card


Curved Horn

+2 damage (See damage calculation for exact step)
Goat Hoof

+0.15 movement speed (See speed calculations)
Mom's Pearl

1/10 additional chance for any given heart drop to become a spirit heart
Cancer

Fire delay decreased by 2 (See fire rate calculations)
Red Patch

1/5 chance to get +3 razor points when taking damage (See damage calculations
for bonus damage)
Lucky Toe

Increases chance to drop an item at the end of the room...

by ~2% with Lucky Foot
by ~10% otherwise

Cursed Skull

Returns you to the previous room when you are hit with 1/2 heart remaining (not
counting spirit hearts) after damage is calculated
Isaac's Fork

1/10 chance to gain a half heart after clearing a room if you have at least 1
heart container. Does nothing for ???.
The Polaroid


Grants 150 frames (5 seconds) of invulnerability when you are hit with 1/2
heart remaining (not counting spirit hearts) after damage is calculated
Grants access to the Chest if equipped while fighting Isaac

A Missing Page

1/20 chance to deal 40 damage to all enemies in the room when taking damage
Pennies


1/2 chance to gain one of the following pickups when picking up any coin

Bloody Penny: Heart
Burnt Penny: Bomb
Flat Penny: Key
Counterfeit Penny: +1 coin (automatic)


These items do not have a chance to be upgraded (see Pickups section)

The Tick


When an enemy spawns, if it has over 60 hp, 15% of that is removed immediately
When you enter a boss room and ?firsttime is not set, you recover 1 heart

Isaac's Head

Creates a familiar that fires projectiles (See Familiars section)
Maggy's Faith

Grants 1/2 eternal heart at the beginning of every level
Judas's Tongue

Items that cost 2 hearts in a deal with the Devil will be reduced to 1 heart
instead
???'s Soul

Creates a familiar that moves around the room
Pickups

Hearts


Chance for a normal heart to become a spirit heart when dropped

Base 1/10 chance
Additional 1/16 chance if you are Eve
Additional 1/10 chance if you have Mom's Pearl
Additional 1/2 chance if you have Mitre


Chance for a normal heart to become an eternal heart when dropped: 1/50
If you are in the super secret room that has an eternal heart in it, all
hearts that spawn in that room will be eternal, i.e., through slot machines
placed with Wheel of Fortune card.
1/2 chance to set col = 2 (full heart vs half?)

Keys


1/20 chance for golden key

Bombs


1/7 chance to set col = 2 (1+1 free?)
1/10 chance to set col = 3 (troll bomb?)
1/50 chance to set col = 5 (homing troll bomb?)
Damage

Base: 10
Mr. Mega: +50


Coins


1/20 chance to be a nickel
1/100 chance to be a dime

Items

How random items are selected


TL;DR: Just seeing an item on the screen means it was removed from that
pool once* and will not be picked again if there were no duplicate entries.
Picking up the item guarantees that it will never show up on your screen ever
again. You do not have to use activated items to guarantee this.

*See note about depleting pools at the end of this section


When does this happen?

When you use the D6, this happens once for each item in the room
When an item is created on the screen. This should mean that items
generated by donating to beggars spawned with the Judgement card will
reflect the room they are in (defaulting to Treasure Room).


Try the following sequence 100 times. If you cannot find an item, default to
using the first pool.

If you're in the library, try the 9th pool

When you choose an item, if ?lib is the item chosen, looks like it tries
to discard it so you don't get double, but it has a bug and it keeps it
anyway.


If you're in the normal Challenge Room, try the 8th pool.
If you're in the Devil Room or ?bummer == 2 or you're in the curse room:

Reset ?bummer to false
If you're in the Angel Room, use pool 10
Otherwise use pool 7


If you're opening a golden chest and you're not in the 11th chapter (The
Chest), use the 6th pool
If you're in The Shop or ?bummer is set

Reset ?bummer to false
Use the 4th pool


If you're in ?boner or ?boner2 with 1/2 chance, try pool 5 (this
doesn't even exist!)
If you're in the Secret Room, try pool 3
If you're in the Boss Challenge Room, use
pool 2
If you're in a boss room

If you're fighting The Fallen, try to select an item from pool 7 that
you do not have
If you're fighting Conquest and don't have White Pony, you get it
If you're fighting Headless Horseman and don't have A Pony, you get it
If you're fighting C.H.A.D and don't have, Little Chad, you get it
If you're fighting Gish and don't have Little Gish, you get it
If you're fighting Steven and don't have both Steven and Little Steve

1/6 chance for Steven (or automatic if you have Little Steve)
otherwise Little Steve


If you're fighting Famine, Pestilence, War, or Death, you get Cube of
Meat
Otherwise, try from pool 2


If none of these are true, try from pool 1


When an item is selected from a pool and passes the itz test, it is removed
from the pool immediately, with the exception of pools 9 (library) and 10
(angel room).
What is the itz test?

This function is called on an item before it is shown to you. If it fails,
then the item is re-rolled.
If you have more than 2 of these, any future picks will be re-rolled.
Note that this does not prevent a boss from guaranteeing a drop, i.e.,
Gish will still drop Little Gish regardless of how many familiars you
have.

Brother Bobby
Sister Maggy
Robo-Baby
Little Gish
Little Steve
Demon Baby
Ghost Baby
Harlequin baby
Rainbow Baby
Abel


If you have the upgrade, the item is re-rolled. You are considered having
the item if you have picked it up at any time.
If you have picked up this item at some point in your save file, there is
a 1/5 chance it will be re-rolled.
Check if it is a "special" item. I have made up this term, since I don't
know what else to group these 57 items as. I believe they are all
non-spacebar items, but there are still some other non-spacebar items not
included in this list. Here are the "special" items:

The Sad Onion
The Inner Eye
Spoon Bender
Max's Head
My Reflection
Number one
Blood of the Martyr
Brother Bobby
Magic Mushroom
Raw Liver
Cupids arrow
Steven
Pentagram
Moms Eye
Distant Admiration
Dr Fetus
Wiggle Worm
Sister Maggy
Technology
Growth Hormones
Lokis Horns
Spider Bite
Lil Chubby
The Small Rock
Super Bandage
Robo-Baby
Little Gish
Little Steve
The Halo
The common cold
The Parasite
The Wafer
Money = Power
Moms Contacts
Ouija Board
Stigmata
Speed Ball
Prayer Card
Ipecac
Tough love
The Mulligan
Technology 2
Chemical peel
Bloody Lust
Epic Fetus
Daddy longlegs
Fate
The Black Bean
Sacred Heart
Tooth Picks
Holy Grail
Dead Dove
Guppys Hairball
SMB Super Fan!
Pyro
3 Dollar bill
Jesus Juice


If it is not a special item, then you get that item
If it is a special item, there is a chance that it will be re-rolled,
equal to 1 - 1/(1.2 + special * 3)

special is a counter that starts at 0
Every time you pick up a special item above, if you did not get it
from a deal with Satan, add 1 to special
For some reason, My Reflection only adds 0.2 to special instead of 1


So basically, these special items become more rare the more of them you
pick up. Below represents the chance that an item in the above list is
re-rolled, assuming that you already have n items from the list.

0: 0.17
1: 0.76
2: 0.86
3: 0.90
4: 0.92
5: 0.94
6: 0.95
7: 0.95
8: 0.96
9: 0.96


Most pools can be exhausted. When this happens, either the first pool is used,
or, in the case of the Boss/Boss Challenge Rooms pool, the Secret Room pool,
and the general-purpose pool (for non-room re-rolled items and beggars) it
bugs out and gives you undefined (flickers through every item).

The Library and the Angel Room never lose items from their pool.
If you deplete item pool 1 to less than 6 items remaining, all 10 pools
will be refreshed to random initial states as they were when the game
started. This does not change what you already picked up.


Incidental item pool removal

All items are stored as numbers, that is, you can have 0 of something, or 1, or
-14, or 3.14, and those are all valid. However, when checking which items are
available to you (i.e., those that you have not picked up yet), it simple checks
to see if it is not 0. This means that some items will be automatically
prevented from showing up through interaction with other items. The following
lists these.

Health Up/Down: <3
Speed Up/Down: Wooden Spoon
Tears Up/Down: Wire Coat hanger!
Range Up/Down: Moms Lipstick
Finishing an Eternal Heart: Lunch
Dead Cat: Dinner
Sacred Heart: Spoon Bender
Ipecac: The Inner Eye
Polyphemus: The Inner Eye
Mutant Spider: The Inner Eye
Spirit of the night: Ouija Board
Dead Dove: Ouija Board
Making a deal with Satan: Lunch
Pretty Fly through slots or pill: Halo of Flies
unknown: Bum friend

Item Pools


Pool 1 (Item Room?)

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
Moms Underwear
Moms Heels
Moms Lipstick
Mr. Boom!
Tammys Head
Moms Bra
kamikaze!
Moms Pad
Teleport!
Doctors Remote
Cupids arrow
Shoop da Whoop!
Magneto
Moms 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 Mush
Rosary
PHD
Xray-Vision
My little Unicorn
Deck of Cards
Ouija Board
Odd Mushroom (Large)
Odd Mushroom (Small)
Dead Sea Scrolls
Bobby - Bomb
Forever alone
Bucket of Lard
Best Friend
Remote Detonator
Stigmata
Bobs 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
Tooth Picks
3 Dollar bill
Telepathy for Dummies
D20
Celtic cross
Abel
Sacrificial Dagger
Rainbow Baby
Blood Rights
SMB Super Fan!
Spider Butt
Daddy longlegs
Guppys Hairball
Skeleton Key (1/2 chance)
The Necronomicon (2/3 chance to be in either pool 7 (additional 1/3 chance), otherwise
here)
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
Monstros Tooth
Lokis Horns
Lil Chubby
The Relic
Sack of pennies
Robo-Baby
The Gamekid
The Book of Sin (2/3 chance)
Little Gish
Little Steve
Little Chad
The Halo
Moms 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)
Moms Contacts
The Bean
Dead Bird
Guardian Angel
Bomb Bag
Moms 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)
NOTE: If under 5 items remain in pool 1, all pools are refreshed as they
were in the beginning


Pool 2 (Boss Room?)

Lunch
Dinner
Dessert
Breakfast
Rotten Meat
One of:

Wooden Spoon
The Belt


Two of: (could be duplicates)

Moms Underwear
Moms Heels
Moms Lipstick


Wire Coat hanger!
Pentagram
Pageant Boy
Cat-o-nine-tails
Stem cells
MEAT!
Magic 8 ball
Moms coin purse
Squeezy
Jesus Juice
BOX
Super Bandage (2/3 chance)
NOTE: Remove the first occurance of all of the above from Pool 1


Pool 3 (Secret Room?)

1up! (1/2 chance for x2)
Raw Liver
Bobs 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 (1/3 chance to be in pool 7, otherwise 1/2 chance to be
here)
Book of Belial (1/3 chance to be in pool 1, otherwise 1/2 chance to be here)
Transcendence (2/3 chance)
Spider Bite


Pool 4 (Shop Room?)

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
NOTE: Remove the first occurance of all of the above from Pool 1


Pool 5

Nonexitent?


Pool 6 (Golden Chest?)

Tammy's Head
One of:

Wooden Spoon
The Belt


One of:

Mom's Underwear
Mom's Heels


Rotten Meat
The Sad Onion
Steven
Fate (1/2 chance)
NOTE: Remove the first occurance of all of the above from Pool 1


Pool 7 (Devil Room?)

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
The Necronomicon (2/9 chance)
Technology (1/5 chance)
Lord of the Pit (1/3 chance)
We need to go deeper! (1/3 chance)
Book of Belial (1/3 to be in pool 1, otherwise 1/2 chance to be in pool 3,
otherwise here)
Lucky Foot (2/3 chance to be in pool 1, otherwise here)
The Nail (2/3 chance)
A Quarter (2/3 chance to be in pool 1, otherwise here)
The Book of Sin (2/3 chance to be in pool 1, otherwise here)
The Common Cold (2/3 chance to be in pool 1, otherwise here)
The Parasite (2/3 chance to be in pool 1, otherwise here)
Money=Power (2/3 chance to be in pool 1, otherwise here)
Moms Knife (2/3 chance to be in pool 1, otherwise here)
Whore of Babylon (2/3 chance to be in pool 1, otherwise here)
Razor Blade (2/3 chance to be in pool 1, otherwise here)
Demon Baby (2/3 chance to be in pool 1, otherwise here)
Forget Me Now (2/3 chance to be in pool 1, otherwise here)
Monster Manuel (2/3 chance to be in pool 1, otherwise here)


Pool 8 (Challenge Room?)

Rotten Meat
Skeleton Key
Boom!
The Compass
Teleport!
Growth Hormones
The Virus
Roid Rage


Pool 9 (Library)

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
Note: Items are never removed from this pool.


Pool 10 (Angel Room?)

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
Note: Items are never removed from this pool.


Specific Items

Dead Sea Scrolls


On use, uses one of the following items:

The Book of Belial
The Necronomicon
Mr. Boom!
Tammys Head
Moms Bra
kamikaze!
Moms Pad
Bobs Rotten Head
Teleport!
Yum Heart
Lemon Mishap
Shoop da Whoop!
Book of shadows
Wiggle Worm
Anarchist Cookbook
The Hourglass
My little Unicorn
Book of Revelations
the Nail
We need to go deeper!
Deck of Cards
Monstros Tooth
The Gamekid
The Book of Sin
Moms Bottle of Pills
The Pinking Shears


The Bible


Using The Bible on the chapter 9 boss (Satan or Isaac) will deal 1000 damage
to the player. According to player damage mechanics, if you have any spirit
hearts or The Wafer, you can survive this.

Dead Cat


If ???, your spirit hearts are set to 1
Otherwise, you get negative Dinner items until you have 1 heart
Sets ?ups[81] to 8
?catlives = 1

Ipecac


If you don't have Inner Eye, sets it to 0.5(?)

Polyphemus


If you don't have Inner Eye, sets it to 0.3(?)

Mutant Spider


If you don't have Inner Eye, sets it to 0.4(?)

Rosary


Augments the 4th (shop?) item pool with The Bible x 7

9 Volt


Instantly recharges current item on pickup

Spirit of the Night


Gives Ouija Board

Dead Dove


Gives Ouija Board

Guppy's Hairball

Each floor, size = round(size * 0.5 + 0.5), lower bounded at 1
Dr. Fetus


Augments the item pool with

Bobby - Bomb x 6
Mr. Mega x 6


Sacred Heart


Gives Spoon Bender

Monster Maneul


Gives one of the following for the room (will not pick one that you already
have):

Brother Bobby
Cube of Meat (Can pick either the 2nd or 3rd form)
Halo of Flies
Distant Admiration
Sister Maggy
Lil Chubby
Robo-Baby
Little Gish
Little Steve
Guardian Angel
Demon Baby
Forever alone


3 Dollar Bill


One of the following random effects each room:

The Sad Onion
The Inner Eye
Spoon Bender
My Reflection
Number One
Lucky Foot
Magneto
Mom's Contact
Ouija Board
Speed Ball
Tough Love


Slots

Unfortunately a lot of this logic appears to be attached to the animation
itself, which makes it impossible for me to see with the source I am currently
using.
Skull Game


4 items (heart, coin, bomb, key) with equal chance

If coin, you get 2-4
Otherwise, you get 2


If you do not have Skatole, 1/13 chance each time to see it
1/3 chance to win, plus extra 1/3 chance if you have Lucky Foot

Slot Machine


Start with a random roll

With Lucky Foot: 3 - 17
Without: 3 - 23


If roll >= 9 and 9/10 chance or ?sloto: roll++
If roll == 7 and 1/3 chance: roll = 10
Check your roll

3:

1/3 chance for Pretty Fly
Otherwise black fly(?)


4: Bomb
5-6: 5 (?)
7: Key
8: Pill
9: A dollar!
10-12: Coins x(1-3)
Otherwise: fail


Fortune Machine


Chance to get a random fortune

0.65 chance normally
0.00 with Lucky Foot


Otherwise, 1/20 chance to explode
Otherwise, 1/30 chance to get Crystal Ball
Otherwise, 1/3 chance to get a card
Otherwise, 1/3 chance to get a spirit heart
Otherwise, you get a trinket

Blood Donation Machine


1/15 chance to break
Otherwise you get 1-3 coins (+1 coin if you have PHD)
When it breaks, you normally get the Blood Bag, but there is a 1/2 chance to
get the IV Bag if you do not have it already.

Beggars?


.col == 31 (devil beggar?)

1/2 chance to...

1/2 chance to get a pill
Otherwise you get a card


Otherwise...

1/4 chance to get a trinket
Otherwise you get a random item


Otherwise (normal beggar?)

1/2 chance to...

1/3 chance to get a 5
Otherwise you get a key or bomb


Otherwise

1/2 chance to...

1/2 chance to get one of the following:

Lunch
Dinner
Dessert
Breakfast
Rotten Meat


Otherwise, you get a card


Otherwise, you get a random item


Rooms and Floors

Spawning


Number of rooms: 5 + chapter * 2.6 + random(0-1), upper bounded at 20
Curse of the Labyrinth: x1.8 rooms
Big floor: +4 rooms

(This part is still being investigated)
Note: You have "full hearts" if your hearts plus spirit hearts equals more
than your maximum hearts.

Sacrifice Room: 1/7 chance, plus additional 1/4 chance if you have full hearts
Library: 1/20 chance, plus additional 1/4 chance if ?bookster
Curse Room: 1/2 chance, plus additional 1/4 chance if ?lastdev (you have
visited the devil in this run?)
Miniboss: 1/4 chance, plus additional 1/3 chance on the first chapter
Challenge Room: Full hearts, not the first chapter, and 1/2 chance if it's the
second chapter (automatic otherwise)
Arcade: At least 5 coins, and an even chapter number (second floor)

Clearing a Room


When determining the chance to get a drop after you clear a room, you start
with a random floating point number between 0 and 1.

If you have the Lucky Foot item, chance = chance * 0.9 + 0.1
If your luck is positive, chance = chance * 0.9 + 0.1
If your luck is negative, chance = chance - luck * 0.1

Woah, woah. Luck is negative, but you're subtracting it from chance.
That means your chance goes up the more negative luck you have!


If you have Lucky Toe

...and Lucky Foot and positive luck stat, chance = chance * 0.98 + 0.02
but not both of the above, chance = chance * 0.9 + 0.1


Something something trinkets to determine drop trixies(false)
If you have Guppys Tail

1/3 chance to guarantee either a brown chest or gold chest with equal
probability
Otherwise, 1/3 chance to guarantee you get nothing


If you have Isaac's Fork, 1/10 chance to gain a half heart
Item boosting trinkets (1/10 chance each):

Ace of Spades: random card
Safety Cap: random pill
Match Stick: bomb
Rusted Key:

1/2 chance to get gold chest
Otherwise you get a key


Child's Heart:  heart


If you didn't get one of the above, check to see where your chance lies to see
what you get

If it is below 0.22, you get nothing

YOU LOSE. GOOD DAY SIR.


If it is between 0.22 and 0.30

1/3 chance to get a card
Otherwise 1/2 chance to get trinket
Otherwise you get a pill


If it is between 0.30 and 0.45, you get a coin
If it is between 0.45 and 0.60, you get a heart
If it is between 0.60 and 0.8 - chapter * 0.01, you get a key
If it is between 0.8 - chapter * 0.01 and 0.95, you get a bomb
If it is above 0.95, you get a brown chest


So, to analyze the above...

Negative luck actually gives you a higher chance to receive an item,
though I'm fairly sure it is a bug. More negative luck will, however, push
your chances of getting a card/trinket/pill off the table.
As you continue through the chapters, the chance to see a key decreases,
while the chance to see a bomb increases.


Super Secret Rooms

Types


Heart pickups
One half Eternal Heart
One Trinket
One Red Chest
Fortune Teller Machine

Devil Rooms

The following conditions are required to have a devil room "spawn" (unsure when spawn is determined, exactly)

Chapter is between 2 and 8. The following cannot have devil rooms

Basement/Cellar 1
Cathedral
Sheol
Chest


?devil != 3 (This is set when the conditions fail, which probably means that
you can't reroll a chance at the devil if you don't get it the first time.
However, this is reset in multiple places, so TBD).
1/x chance or ?satan. Chance is determined as follows:

Base chance starts at 0.01
If you have the Pentagram item, add 0.20 chance
If you have a second Pentagram (somehow), add 0.10 chance
If you are holding Book of Belial, add 0.25 chance
If you are holding Book of Revelations, add 0.35 chance
If you killed a "bum" at all this game, add 0.35 chance
If ?bossdmg, add 0.35 chance

?bossdmg is set true when you start the game
?bossdmg is set false when you get hurt, if:

You have no spirit hearts
f2 <= 200 (Certain damage sources don't count?)


If ?devil, add 0.99 chance
If the last devil room you've seen was on the previous floor, multiply the
chance by 0.25
If the last devil room you've seen was two floors ago, multiply the
chance by 0.5


Additionally, Krampus will spawn in the devil room with a 1/10 chance, plus an
additional 1/3 chance if you made a deal with the devil already. He will not
spawn more than once.
Angel Rooms

The following 3 conditions must be true for a Devil Room to spawn as an Angel
Room instead (note the spawn conditions still rely on the above Devil Room
conditions)

1/2 chance
You did not make any deals with the devil
A devil room "spawned" at least once (Interesting note: This variable is not
reset, so if you see a devil room in one game, you can start another game and
see an angel room as early as your second floor.)

Deals with the Devil


1/5 chance that the item costs 3 spirit hearts
Otherwise, the following items cost 2 heart containers and all others in item
pool 7 cost only 1 heart container

The Mark
The Pact
Lord of the Pit
the Nail
Dead Cat
Demon Baby
Whore of Babylon
Brimstone
Bloody Lust
Spirit of the night
Guppys Head


If you have Judas' Tongue, the above items cost 1 heart container, but those
that cost 3 spirit hearts will still cost as much.
If the item costs 3 spirit hearts and you do not have at least that many, you
cannot take it.
If the item costs heart containers

Your maximum hearts is reduced by the cost
You suffer damage equal to cost - max_hearts_before + current_hearts

Because your spirit hearts are not removed but are restored, you will
not suffer damage and thus cannot die if you have any spirit hearts
If you do not have spirit hearts and have heart containers equal to or
less than the deal, you will die from damage. Two notes:

In the Womb and beyond, you always take 1 heart of damage, which
may kill you.
If you have the Wafer, you will always take 0.5 hearts of damage.
This item can actually get you killed when you otherwise would be
safe.


If you have non-negative hearts, your spirit hearts will be restored to
what they were before the deal
If you are negative on heart containers, your spirit hearts are stripped
and you are dealt 10 damage. It almost seems like you shouldn't survive
this, but fortunately they forgot to reset your grace period, so the
damage you took before makes you invincible to this 10 damage, and you
survive. At this point, you can still bring yourself out of negative
hearts by picking up enough health up items.


Mini-boss Rooms


Seven Sins

Drop rate on items:

If "super" version: 1/7
Otherwise: 1/28


Otherwise, you get the pickup listed first
Sloth

Card
Bobs Rotten Head
(Super) Bobs Curse


Lust

Pill
The Virus
(Super) Yum Heart


Wrath

Bomb
Mr. Boom!
(Super) Mr. Mega


Gluttony

Heart
<3
(Super) Bucket of Lard


Greed

Coins (x4-8)
Steam Sale
(Super) A Quarter


Envy

Troll Bomb
Shoop da Whoop!
(Super) Forever alone


Pride

Card
Anarchist Cookbook
(Ultra) Dead Cat (bugged to get Pill instead?)


Greed has a chance to spawn in the...

secret room if:

You are in chapter 5 or greater
1/3 chance


shop room if:

You are in chapter 4 or greater
1/(6 - chapter) chance

Chapter 4: 1/2 chance
Chapter 5-6: 100% chance


Greed will not spawn in one of these rooms if

a mini-boss room is already picked
he spawned in one of these in the previous chapter N.B. XL floors,
particularly Depths/Necropolis XL count as two chapters ahead, so this
part will not apply
he spawned in the other of these two rooms


Boss Rooms


The Fallen has 1/10th chance to spawn if a Devil Room has spawned before
If you use Book of Revelations and you're on a non-XL floor in Womb or before,
you will get one of the four horseman as your boss.
Normal boss selection procedure:

1/5 chance to get one of the four horseman respective to your level
If you got a horseman from random selection or Book of Revelations, 1/10
chance to get The Headless Horseman instead
Otherwise, if you're on Womb/Utero 1 with 1/3 chance:

1/2 chance to get 38
Otherwise 41


Otherwise, if you've visited the devil at some point, 1/10 chance to get
The Fallen
Otherwise, if you're on Womb/Utero 1 with 1/3 chance, you get either 30
or 33 with equal chance
Otherwise, if you're on the second floor of Cellar or Catacombs with 1/4
chance:

1/2 chance to get

Cellar: 28
Catacombs: 36


Otherwise

Cellar: 32
Catacombs: 27


Otherwise, if you're on the first floor with 1/5 chance:

Basement/Cellar: 13
Caves, Catacombs: 14
Depths, Necropolis: 15
Womb, Utero: 16


Otherwise, if you are on the 3rd chapter or Cellar with 1/4 chance:

Cellar: 13
Caves, Catacombs: 14


Otherwise, for chapters 1-3 with 1/2 chance:

Basement 1: 2
Basement 2: 3
Caves 1: 4
Cellar 1: 37
Cellar 2: 29
Catacombs 1: 26


Otherwise

Basement 1: 1
Basement 2: 2
Caves 1: 3
Caves 2: 4
Depths 1: 5
Womb 1: 7
Cellar 1: 34
Cellar 2: 37
Catacombs 1: 29
Catacombs 2: 26
Necropolis 1: 30 or 35
Utero 1: 31


Curses


You cannot get a curse on 11th chapter (chest)
1/x chance to get Curse of the Labyrinth if applicable (first floor of chapter)
1/2x chance to get Curse of the Lost
1/2x chance to get Curse of Darkness
x =

80 when you start playing
30 after you kill Mom
10 after you unlock Everything is Terrible
5 after you complete Cathedral on one character


So, a fully unlocked game has a

1/5 chance to get Curse of the Labyrinth (when applicable)
~1/10 chance to get Curse of the Lost
~9/100 chance to get Curse of Darkness


Objects

Red Chest


1/10 chance to get one of the following items:

Dead Cat
Guppys Tail
Guppys Paw
Guppys Head
The Mark


If you already have the item or did not get the roll, you have a 1/18 chance
to be teleported to the Devil or Angel room
Otherwise, you have a 1/5 chance to spawn 2 spiders
Otherwise, you have a 1/5 chance to spawn a super troll bomb
Otherwise, you have a 1/5 chance to get 3 blue flies
Otherwise, you get a random choice of:

2 pills
2 troll bombs
2 spirit hearts (1/2 chance to get only 1)


Brown Chests, Gold Chests, and Tinted Rocks (?)

This is really confusing, sorry! A lot of these are unknown items, and the
process is really random. I'm also not sure where spirit hearts come in with
respect to tinted rocks, since they obviously drop a lot.

First you roll how many pickups you will get

frame 8 and .col == 1: 1-2 pickups (brown chest?)
frame 6: 1-8 pickups (min 2) (gold chest?)
Otherwise: 1-4 pickups (min 2) (tinted rock?)


2/3 chance

Check trinkets to see if you will get a pickup (see "Clearing a Room"
under "Item boosting trinkets")
If you have Lucky Toe or got an extra pickup above, add +1 to your pickups


Starting at 0, loop until you pass your pickup number

If you had a trinket proc for an extra item, you get that immediately
Otherwise

You get treasure (an actual item) if

It is the first time in the loop (so that means using one of the
bonus item trinkets prevents objects from yielding treasure!)
One of the following rolls:

1/10 chance if it is a rock (?trg == 2?)
1/5 chance if it is frame 6 (gold chest?)


If you didn't get treasure, 1/5 chance on a non-rock to...

frame 6: you get a card
Otherwise (brown chest only?) you get a pill
Another 1/2 chance to get a trinket in addition to either


If you got either of the two above treasures, you stop
Otherwise, roll a random floating point number from 0-1...

For chests

0.00 to 0.35: 1-3 coins
0.35 to 0.55: 5

Additional 1/2 chance to get -1 pickup


0.55 to 0.70: you get a key
0.70 to 0.71: (first loop only) you get a brown chest and you stop
0.71 to 0.72: (first loop only) you get a gold chest and you stop
0.72 to 1.00: you get a bomb


For tinted rocks

0.00 to 0.60: 5

Additional 1/2 chance to get -1 pickup


0.60 to 0.70: you get a key and you stop
0.70 to 0.71: (first loop only) you get a brown chest and you stop
0.71 to 0.90: (first loop only) you get a gold chest and you stop
0.90 to 1.00: you get a bomb


If frame 8 and .col == 1 (brown chest bonus loot?)

1/2 chance: 1-4 coins
Else, you get 5


Tinted Rocks


Each room has a random number rolled from 65 to 180 (range of 115). This
number corresponds to a specific tile, the top-left being 48 and the
bottom-left being 191. If there is a rock on the randomed tile, then it
becomes a tinted rock.
You can assume that the chance that there is a tinted rock in any given room
is number_rocks / 115, excluding the rocks from the first and last row(?).

Poop


Any given poop has a 1/40 chance to spawn as poop with flies
Some rooms spawn poop with flies intentionally
Any poop with flies has a 1/20 chance to spawn as golden poop
Golden poop spawns

Counterfeit penny with 1/3 chance
Otherwise between 5-8 coins


Misc

Challenge modes


Dark was the Night

100% chance to get Curse of Darkness each floor


7 Years Bad Luck

Luck stat starts at -2
1/3 chance for no treasure room each floor


Large Marge

100% chance to get Curse of the Labyrinth each floor


9 Deaths

Start with Dead Cat


Lord of the Flies

Start with The Mulligan, Infestation
No treasure rooms


The Doctor's Revenge

Start with Dr Fetus, Doctors Remote
No treasure rooms


Meat 4 Evar!

Start with Cube of Meat (x4)
No treasure rooms


Spider Boy!

Start with Mutant Spider, Spider Bite
No treasure rooms


Isaac was Good Today

Start with The Halo, Holy Grail
No treasure rooms


The Purist

No treasure rooms


Player Damage Taken


Everything after chapter 6 (Womb+) does at least 1 heart
If you are holding The Wafer, damage is always exactly 0.5 hearts. This also
includes all deals with Satan(?!)
If you are fighting Satan in Sheol, ?plh is set true (possibly just
cosmetic)
You can avoid damage if:

You are in your grace damage period

This is 30 frames per half heart of damage taken

A half heart of damage gives 1 second of invulnerability
A full heart of damage gives 2 seconds of invulnerability


You get 3 seconds of invulnerability if the hit activates Whore of
Babylon.


You are literally not visible
You have an invulnerable effect

Celtic Cross has 1/5 chance to shield for 200 frames (~7 seconds)
The Polaroid shields for 150 frames (5 seconds) if your health is
below one half when you take damage
Book of Shadows shields for 300 frames (10 seconds) on use
Chariot card and My Little Unicon last 180 frames (6 seconds)
The Gamekid lasts 200 frames (~7 seconds)


?horse > 0 (Using either of the Pony items' activated abilities)
?dec > 0 (Something about Best Friend?)


You lose credit for the "no hits taken" achievement when

You take damage from an enemy
You make a deal with Satan


You do NOT lose credit for the "no hits taken" achievement when

You use a blood donation machine
You help a devil beggar
You take a Bad Trip! pill
You use the Razor Blade item
You use the Blood Rights item
You use the IV Bag item


If your normal and spirit hearts are 0, you are dead, unless

You do any of the above with spirit hearts remaining, with the exception
of Razor Blade. That can and will kill you.
You took damage from a deal with the devil under certain conditions (TODO)


If you have any spirit hearts remaining, you will not lose any actual hearts,
even if you take 1 heart of damage with a half spirit heart left.
If you take health damage and ?devil is not 2 or 3, it is set false (I
believe this refers to if the state of the devil room has not been determined)
If you have Infestation, 1-3 blue flies are spawned
If you have Fish Head, 1 blue fly is spawned
If you have a total of one half of either hearts or spirit hearts

With the Umbilical Cord trinket, you gain Little Steve for the remainder
of the room
With Scapular, you gain one spirit heart and temporarily lose Scapular
until the next room


If you have Red Patch, 1/5 chance to get 3 razor points
If you have A Missing Page, 1/20 chance to deal 40 damage to all enemies
If you have Habit, you gain half of a charge
If you have Celtic Cross, 1/5 chance to gain a shield for 200 frames (~7
seconds)
If you have The Black Bean, you create a damaging fart
If you are currently at one half heart

If you have Whore of Babylon and it was not activated yet, it is triggered
If you have The Polaroid, you gain a 150 frame shield (5 seconds)
If you have Cursed Skull, you are teleported to the last room


Everything is Terrible


Increased chance to get a curse (see above)
Chance to ______ changed from 1/10 to 1/5 (something during creation of
something, setting its specoz to something. My guess would be the chance to
get a special version of a creature or possibly boss)

Source Notes

These are my notes on the source code as I have been reading it.
Global Variables


ups: Added upgrade
fmode: Fired projectile model
hmode: Head model
bmode: Body model
sk: Skin color(?)
kogs: Items that are going to be dropped (array of item codes)
cowss: Coins that are going to be dropped (int for count)
itc: Current item charge
iter: Stored charges for each item type(?)
colit: Currently held item id
eta: If you have a half eternal heart (bool)
skiner: Selected character code (isaac, maggy, etc.)
wiptz: Reduces chance for some items to drop
chaps: Something to do with chapters?
fra: Something to do with frame count?
Room (_root.lev == _root._____)

cus: Curse room
chamb: Challenge Room
gamb: Arcade
166: Devil Room
169: I AM ERROR


Room modifiers

altch: Boss Room


_x_mode changes


I originally started recording this, but I believe this is fire, head, and body mode. Not very relevant.
?fmode

Sad Onion: 2
Inner Eye: 3
Spoon Bender: 4
Max's Head: 5
My Reflection: 6
Number One: 7
Blood of the Martyr: 8
Polyphemus: 20
Mutant Spider: 23
Tough Love: 24


?hmode (= ?fmode?)

Chemical peel: 38
3 Dollar Bill: 44
SMB Super Fan: 42
Sacred Heart: 41
Polyphemus: 40
Speed Ball: 35
Spirit of the Night: 39


?bmode

Mom's Purse: 20
SMB Super Fan: 27
BOX: 26
The Black Bean: 24
Spirit of the Night: 22


Item codes


5: ?
5.01: Heart

003: Spirit Heart
004: Eternal Heart


5.02: Coin
5.03: Key

003: Golden Key (?)


5.04: Bomb

003: Troll bomb
005: Super troll bomb


5.05: Brown Chest
5.06: Gold Chest
5.07: Pill
5.08: Slot machine / Fortune teller
5.09: Trap door
5.1: Item
5.3: Card
5.34: Ending chest
5.35: Trinket

Monster codes


18: Angry fly

??? Codes

Unsure if these are bosses, monsters, or neither

46: Sloth
47: Lust
48: Wrath
49: Gluttony
50: Greed
51: Envy
52: Pride
53: Krampus

Boss codes


22: Headless Horseman(?)
24: Satan
30: (Womb 1 boss)
33: (Womb 1 boss)
38: (Womb 1 boss)
39: Isaac
40: ???
41: (Womb 1 boss)

Other notes


Whore of Babylon (ups[122]) is set to true in the global ups, but then set
to false in the local ups if you don't have the heart requirements.
To get spacebar code from item code

If item_code < 55: spacebar_code = item_code - 32
else: spacebar_code = item_code - 40


To get item code from spacebar code

If spacebar_code >= 18 or spacebar_code == 16: item_code = spacebar_code + 40
else: item_code = spacebar_code + 32


Credits


[1] Speedytech7 for tutorial on extracting the SWF from the executable
[2] Igor Kogan for Flare: free software to decompile the SWF to ActionScript
[3] Xaiter for painstakingly creating a list of all the codes and their corresponding name
[4][5] ForteGSOmega for the work he did as a way to sanity-check and understand some more difficult parts