The Book of Sin is an unlockable activated item.
A black book with the number seven written in red ink on the cover, with some splotches around the seven.
- Full Hearts
- Bombs or bomb variant (1+1 Free, Troll Bomb, or Mega Troll Bomb)
- Tarot Cards
- Soul Hearts
- Keys or Golden Keys
- As with most activated items, items such as Habit, 9 Volt and The Battery decrease the charge time, increasing the effectiveness of this item.
- Pill-related items such as PHD or Lucky Foot work well with this item, as they prevent the player from receiving negative pill effects.
- Trinkets such as Bloody Penny, Burnt Penny, Flat Penny and Counterfeit Penny work well with this item, as picking up coins spawned by this item while holding any of these Trinkets give the chance of receiving an additional item.
- You can farm pick ups from this item and Habit by using the Blood Donation Machine or a Demon Beggar. However, this is risky as this item does not always give Hearts, and the player could potentially lose more hearts than they started with. But the Blood Donation Machine could give you Blood Bag after a few attempts. (Or the less desirable IV Bag that does not give hearts)
- Some believe that each pickup represents one of the seven deadly sins:
- Whole Heart: Gluttony
- Bomb or bomb variant (1+1 Free, Troll Bomb, etc.): Wrath
- Pills: Lust
- Random Coin: Greed
- Tarot Cards: Sloth
- Soul Heart: Envy
- Key: Pride