Mysterious Paper is an unlockable trinket.
- Upon hit, has a small chance to activate the A Missing Page5% chance to induce The Necronomicon's effect upon taking damage. effect. (Probably the same chance as the Missing Page itself)
- Upon taking damage at one half red heart or less, there is a moderately common chance to trigger the effects of either The PolaroidIf 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. or The NegativeIf 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. Also allows entrance into the Dark Room..
- Small chance to take the player to the Chest or the Dark Room without The Polaroid or The Negative.
- Small chance to display a puzzle piece on Isaac's Last Will in the same way as the Missing Poster.
- Small chance to revive Isaac as The Lost upon death in the same way as the Missing Poster.
- It seems that the Mysterious Paper randomly imitates the effect of a paper item when appropriate. Unlike the 3 Dollar BillGives Isaac a random tear effect every room.
The effect given changes upon entering a room.
The effect changes every 3 seconds., the Mysterious Paper does not choose which effect it will have in the current room. Rather, it seems to randomly decide whether a particular effect will activate when relevant. It is theoretically possible that the Mysterious Paper can also sometimes provide the effects of Bogo BombsAll standard bomb pickups become 1+1 bomb pickups., Humbling BundleGives one extra pickup (1+1 Free version) of Red Hearts, pennies, bombs, and keys. Does not work with blue, black, and half red hearts, nickels, and dimes., Contract From BelowDoubles the number of pickups and chests spawned after clearing a room or performing some other triggering action (such as using a blood donation machine), but reduces the chance for any pickups to spawn at all., Bible TractIncreases chance for Eternal Hearts to spawn., and Store CreditThe next store purchase is free. The trinket disappears on purchase., though this has yet to be proven true.