Missing No.

Missing No. is an unlockable passive item.

Effects

 * Randomizes passive items and stats on pickup and at the start of every floor.
 * Stats gain a random flat modifier. These modifiers do not stack between levels and are instead rerolled every time.
 * Speed -0.2, 0 or +0.2.
 * Range -0.5, 0 or +0.5.
 * Tears -0.5, 0 or +0.5.
 * Shot speed -0.2, 0 or +0.2.
 * Damage -1, 0 or +1.
 * Luck -1, 0 or +1.
 * Does not affect trinkets, cards, pills, pretty flies, /, Key Pieces, or active items.
 * Causes but does not remove transformations.
 * Missing No. cannot be re-rolled with or  after being picked up.

Strategy

 * There is no real strategy to Missing No. as it randomizes all the player's items. The benefit of the randomization can be added by collecting more items to increase the chance of a good item synergy.
 * However, this item can be used to gain more health if desperately needed, as the randomization does often include items that grant you various types of hearts.
 * If the player has already obtained a large number of items (such as during a run where they have gained infinite money in greed mode), it is highly recommended to avoid this item, as it will almost always end up rerolling all the items the player has thus far collected into.

Trivia

 * This item is a reference to the infamous Missing No. glitch occuring in the first Pokémon games. The glitch would often corrupt save files, and therefore randomize various parts of the game as it would use the incomplete index values attributed to entities not included in the final release of the game. Isaac's appearance when affected by Missing No. is based on this glitch which could cause the player's sprite to become scrambled.
 * The item also resembles the painting "Composition with Red, Yellow, and Blue" by Dutch painter Piet Mondrian.
 * The background color for the Missing No. achievement has the same color as all the challenge unlocks. This implies that Missing No. was originally intended to be unlocked via a challenge. (Or, perhaps, it was intended to be looked at as an error.)

Seeds
FTTQ E3RZ - Secret room directly to the right of the starting room X1F3 19X9 - First floor secret room to the left of the shop 2QDT ALD2 - First floor secret room to the bottom of the treasure room W4Q7 JMMP - First floor secret room directly under the treasure room