Eve starts with this item after unlocking it and donating 439 coins to the Greed Machine.
Both conditions must be met in order for Eve to hold it; donating 439 coins before defeating Satan with Eve will wrongly state on Eve's profile on the Character Selection Screen that she has it equipped.
Damages all enemies in the room, but deals a heart of damage to Isaac with each use.
or Blood Donation Machines, red hearts are removed before soul or black hearts, meaning you can still use it if you have a single red heart container and soul hearts. This also means that players should avoid using this item if they plan on keeping an eternal heart, as activating the item will remove it as well.
Like similar items mentioned above, use of this item does not affect Devil or Angel room chances.
If the character has half a red heart or no red hearts after taking damage, it triggers the Book Of Shadows effect, creating a shield that nullifies all types of damage for 5 seconds. Also allows entrance into The Chest.
: Isaac takes no damage while invincible, allowing for repeated free uses of the item.
Increases damage and speed whenever Isaac has half a red heart or less (one red heart for Eve), ignoring any soul or black hearts.
: The Razor Blade can be used to activate this item's effect by doing enough damage to get Isaac down to half a red heart (or one red heart as Eve), providing a big damage boost for the current room at the cost of health.