I was on a run and entered a devil room, for 2 red hearts was a black book with a pentagram on it. I didn't want to sacrifice the 2 hearts for an item I didn't need or possibly didn't want.
Does anyone know what it does?
3 Answers
Its the satanic bible, on usage, gives you a black heart
If you mean this one:
it's the Satanic Bible, and gives Isaac a black heart when used. A behaviour similar to the Book of revelations.
It's an evil item, so probably it increases the chance of spawning a devil deal room.
Source here.
4There are two books with pentagrams in the game.
If the book has a black pentagram on it, it is the Book of Belial. It's a 3-room charge, and gives you +2 damage for your current room. It also has the nice bonus of giving you a 100% Devil/Angel room chance, and all Devil/Angel rooms stay open forever.
If the book has a red pentagram on it, it is the Satanic Bible. It's a 6-room charge, and gives you one black heart on use.
This website may be helpful for you in the future.
