The Negative

The Negative is an unlockable passive item.

Effects

 * If the character has half a red heart or no red hearts after taking damage, it triggers The Necronomicon effect, damaging all enemies in the room.
 * Allows entrance into the Dark Room after beating Satan in Sheol by touching the chest.

Trivia

 * The Negative allows access to the Dark Room, which is also the name of a room used to develop photos.
 * A negative is a piece of film that's been used to take a picture but hasn't been developed into a finished picture. A negative has inverted hues as well as inverted lightness.
 * Because of the instant nature of Polaroid film versus regular film, however, one would usually never see the Negative of a Polaroid and a darkroom would not be required to develop one, which calls into question its relation to The Polaroid. However, this could probably explain the fact both items can't be picked up together in a run (unless Forget Me Now or a 5-pip Dice Room is used).