Finally some item spawn mechanics. The following applies for item spawning after you've cleared the room.

Quick notes about some things: Luck is relevant for this part and, apart from Tough Love teeth, for this part only. This is also the

**only** time Lucky Toe is relevant, while Lucky Foot has other uses.

**Dropping Stuff**1. Check if the related trinkets activate:

Ace of Spades: 10% Chance to replace drop with a tarot card (80%) or a deck card (20%)

Child's Heart: 10% Chance to replace drop with a heart item

Matchstick: 10% Chance to replace drop with a bomb item

Rusted Key: 10% Chance to replace drop with a key (50%) or a golden chest (50%)

Safety Cap: 10% Chance to replace drop with a pill

Note: At least something has to drop for the trinkets to activate in step 3.

2. Check if Guppy's Tail activates (will override results of the above checks)

33% chance to drop a normal chest (50%) or a golden chest (50%), skip step 3

22% chance to drop nothing/prevent something from dropping

45% chance for nothing to happen. In that case, go to step 3

3. Check for normal drops.

Here's a handy table which outlines the chances for basic items:

http://pastebin.com/Hf6tMUhL

Behind the scenes (why trinkets etc have a crappy chance of dropping with max luck stuff):

The game picks a random decimal number x between 0 and 1.

For each luck factor, x is set to "0.9 * x + 0.1"

I.e. for 3 luck factors, the new x is "((0.9 * x + 0.1) * 0.9 + 0.1) * 0.9 + 0.1 = 0.729 * x + 0.271"

Now, x has to be between 0.22 and 0.3, which is only possible if the original x was 0.04 (4%)

If the x was in the correct range, there's a 33% chance each for a trinket/card/pill (which results in the 1.33%)

**Item Quality**After the actual drop was determined, what's left is the quality.

Trinket: Equal chance for any yet (in this playthrough) unseen trinket. If you've already seen all trinkets, drop a card instead.

Card: 80% chance for a tarot card, 20% for a deck card.

Pill: Random

Coin: Normal coin, can be upgraded: 5% nickel, 1% dime

Key: Normal key, can be upgraded: 2% golden key

Chest: Always normal chest

Bomb: Normal bomb, can be "upgraded": 14.3% 1 + 1 free, 10% normal troll bomb, 2% super troll bomb

Heart:

1. Try to make it a soul heart:

It has a 10% chance of happening normally (when neither of the below is true)

It has a 15.63% chance of happening when playing as Eve

It has a 19% chance of happening when you have Mom's Pearl

It has a 55% chance of happening when you have The Mitre

2. If 1. failed, try to make it an eternal heart with a chance of 2%

3. If 2. failed, try to turn it into half a heart (yes, that's considered an upgrade) with a chance of 50%

4. If all of the above failed, a normal heart is dropped.

Reminder: Mom's Pearl and The Mitre do nothing else.

By the way, Isaac's Fork is processed around here as well, which means there's a 10% chance of recovering half a heart after clearing a room. I only saw the percentage and called it a day when checking the first time (I'll try not to blindly rely on the wiki in the future)

Edit: Forgot negative luck. That's behaving really strangely. After getting the x (from "behind the scenes"), it is decreased by luck * 0.1, which means it's actually increased (since luck is negative).

For the "bad luck" challenge, this means:

Chance of Nothing is decreased to 2% while chance for a normal chest is increased to 25% (without factoring in the luck factors etc).

That can't be intended.

Edit2: I left it out because the change is insignificant and would make the table confusing, but each level, key items get -1% chance while bombs get +1% chance

"Naturally, I knows the hacker" - Kid, Ever17