So I have been playing The Binding of Isaac, and you can have red hearts, and blue hearts (Known as Soul Hearts) and I was wondering, does using the Curse Room Door or doing deals with the devil prioritize your red hearts or soul hearts first?
Both Whore of Babylon and Devil Room transactions only care about red hearts. The only exception is that Devil Room transactions adapt to use soul hearts when playing as ???.
Whore of Babylon
I'm not sure what the "Whore Of Babylon Door" is. If you meant the Whore of Babylon, it only activates based on remaining red hearts:
If you have a half-heart left, a message reading "What a horrible night to have a curse." appears on the screen and the player becomes the Whore of Babylon
...he will stay in that form until leaving a room with more than a half-heart (soul hearts do not count.)
If ??? picks this up, he permanently gains its effects upon leaving the room for the remainder of the game.
The reason ??? permanently gains the effect is because he doesn't get red hearts.
As for devil room transactions:
The costs will always take the exact cost in red heart containers and consumes all soul hearts when you try to overspend, except when playing as ??? for whom the costs are converted to soul hearts.
- When playing as ???, all items will cost 3 Soul Hearts.
- If the player has no Soul Hearts and buys an item for exactly as many or more red heart containers than they currently have, Isaac will die.
- If the player has Soul Hearts and buys an item for more red heart containers than they currently have, Isaac will lose all heart containers and Soul Hearts, and will die from a single hit until more Soul Hearts or heart containers are collected.
- If the player has Soul Hearts and buys an item for exactly as many red heart containers as they currently have, Isaac will keep his Soul Hearts.
- Without any heart containers, the gameplay functions exactly like ???, making red hearts and red heart-related items useless until more heart containers are obtained, along with other special effects such as Whore Of Babylon always being active.
- Eternal Hearts are ignored when making deals, and they will remain when Isaac's health is set to 0.
- Judas' Tongue sets the price of all Devil Room items to 1 heart container, but all soul heart deals will remain the same.
- Invincibility granting items such as Book Of Shadows will not make the items free of health costs, unless you are playing as ???, whereas items that grant invincibility will allow you to "steal" Devil Room items. However, they will prevent Isaac from dying if he has no Soul Hearts.
- Temporary health boosts such as those from the XI Strength Tarot Card or Liberty Cap will not reduce the number of heart containers lost from a deal. Going out of the room will remove the extra heart container, if any
There are also some related bugs
- If you are playing as ??? with The Wafer, buying any item for Soul Hearts will only cost half a Soul Heart, instead of 3 Soul Hearts.
- Any invincibility-granting item can allow you to buy items that cost Soul Hearts for free, as long as you have at least 3 Soul Hearts.
- If you use momentum and grab both items while moving, it will take the heart container payment for both while only giving you the first Item.
Whore of Babylon only counts "real" hearts. If you have 1 red heart or less, you get the effect, no matter how many soul hearts you have.
Deals with the devil can only take away red hearts (remember this is a permanent loss), unless you are playing as ???. You can lose all your hearts this way- you will survive as long as you have soul hearts. Attempting to trade more hearts than you have will kill you, no matter how many soul hearts you have.