Missing Poster

The Missing Poster is a trinket.

Effects

 * If Isaac dies in a Sacrifice Room while holding it, a particular puzzle piece will be displayed as cause of his death on his last will.
 * Dying in a Sacrifice Room while holding it will outright unlock The Lost, regardless of current character.
 * If Isaac dies holding this trinket and has already unlocked The Lost, he will be revived as The Lost and Missing Poster will be consumed.
 * If The Lost dies holding this trinket, he will be revived in the room he was before and Missing Poster will be consumed.

Puzzle Pieces

 * The puzzle piece will belong to one of four jigsaw puzzles. To which one is indicated by a tiny grey symbol to the top left of the piece.
 * The symbol can either be a pixel, a 2x2px square, a 3x3 px square, or four pixels arranged like a plus-sign.
 * Each jigsaw puzzle displays an altered last will for the characters Isaac, Maggy, Judas, or Azazel respectively.
 * Each picture on the last will shows in which way Isaac has to die when playing as the respective character in order to unlock The Lost.

Trivia

 * The first scene in Ending 15 shows The Missing Poster pinned to a utility pole, with a silhouette of Isaac's mother who seems to be searching for Isaac in the background.
 * There are many puzzle pieces in total. Assembling all of the jigsaw puzzles and figuring out what they meant was initially designed to be collaborative effort of the community.