Undefined

Undefined is an unlockable activated item.

Effects

 * Teleports Isaac to the Treasure Room, the Secret Room, the Super Secret Room or I AM ERROR. There is also a minuscule chance of teleporting into a Black Market.
 * The chances for each main destination are equal.
 * Has no effect when used in.

Strategies

 * The I AM ERROR room in and  will have a beam of light/trap door leading to the next floor, even if Isaac doesn't have  or.
 * and are reset on exiting the I AM ERROR room, which can be done repeatedly as long as the player can gather enough charges to successfully warp to it. This can provide a ridiculous number of items from the golden chests in.
 * This makes it possible to kill ??? or Lamb multiple times. If Isaac has an item that resurrects him as a different character, multiple achievements and items can be unlocked in a single run.
 * is also reset and can be cleared repeatedly.
 * As no Secret Rooms or Super Secret Rooms spawn on any floor during the Ascent, this item will only warp Isaac to either the Treasure Room or the I AM ERROR room. This can be a reliable method of gaining many items on the way up to, while also allowing the player to skip potentially difficult encounters.

Trivia

 * The item is a reference to a bug in the original The Binding of Isaac, where exhausting an Item Pool (or rarely simply by chance) would cause an item to spawn whose name and description was listed as "Undefined", and whose sprite would rapidly cycle through the sprites of every other item in the game. Undefined by itself creates no effect, but if it was ever picked up, should the game attempt to spawn an item from an exhausted item pool, the game instead crashed, as it could no longer spawn Undefined. From Rebirth onwards, an exhausted item pool will instead spawn, even if the item would normally never spawn from that item pool and/or Breakfast had already been obtained in the run.
 * In programming "Undefined" refers to an unknown value.
 * Given the Glitch theme of the item and the ability to access Chapters that have not yet been unlocked using I AM ERROR, along with the ability to acquire mass upgrades in The Chest and The Dark Room, it is possible that it was intentionally made into a powerful sequence-breaking item.
 * The sprite for Undefined appears to be, fittingly, a glitched and spliced version of other item sprites, with the bottom right part noticeably being the, the bottom left being the , and the top half being . This may also be a reference to Undefined's sprite in the original The Binding of Isaac.

Seeds
TRP0 FE16 (first treasure room, adjacent to spawn) 9YDH V6SL (first treasure room, adjacent to spawn) F189 W42E (first treasure room, adjacent to spawn. Teleports to I AM ERROR room upon first use in hard mode.) 0JGY 6ZWX (first treasure room near spawn) W0WZ QCRJ (first treasure room, adjacent to spawn) 6AGC GCCH (first treasure room, adjacent to spawn) SJKJ XZB2 (first treasure room, adjacent to spawn) 4CG9 42ED (first treasure room, adjacent to spawn) YAD2 KJCM (first treasure room, adjacent to spawn) 8LQF 7MT0 (first floor treasure room)