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 effect, damaging all enemies in the room.
 * Allows entrance into the after beating Satan in  by touching the chest.
 * +1 damage.
 * Opens A Strange Door in II and its variants that leads to / II.
 * Unlike with the Dark Room entrance, The Negative gets consumed by the door and vanishes from Isaac's inventory.

Synergies

 * r / : Increases the damage from 40 to 80.
 * A Missing Page + Missing Page 2: The damage increase stacks for a total of 120 damage.

Trivia

 * The Negative allows access to the Dark Room, which is also the name of a room used to develop photos (Darkroom).
 * A negative is a piece of film that's been used to take a photograph but hasn't been developed into a finished photograph. 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 dark room would not be required to develop one, which calls into question its relation to . However, this could probably explain the fact that both items can't be picked up together in a run (unless or a 5-pip Dice Room is used).