D1

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(except in Rebirth and Afterbirth)

D1 is an unlockable activated item added in The Binding of Isaac: Afterbirth †.

Effect

  • Upon use, duplicates one random pickup in the current room, including Cards, Runes, Chest.pngChests, and trinkets.
  • (in Repentance and Repentance+) Duplicated pickups may not be identical to the original; for example, a duplicated card may be a different one than the original.

Notes

  • It is possible to duplicate ShopShop pickups that have not been purchased yet.
  • With Collectible Car Battery icon.pngCar Battery, it is possible to infinitely generate Lil' Battery.pngLil' Batteries from a single Lil' Battery.
    • (in Repentance and Repentance+) While it's still possible to generate infinite batteries with this synergy, it is slow to do so since mostly Micro Batteries will spawn. The occasional Lil' Battery or other battery spawn is needed to build up the battery pile.
  • (except in Repentance and Repentance+) Rune of JeraRune of Jera can not be duplicated.
  • (except in Repentance and Repentance+) Mimic chest Repentance.pngMimic Chests will not be duplicated until their spikes are exposed.
  • (except in Repentance and Repentance+) Opened chests will be duplicated into an unopened copy.
  • (except in Repentance and Repentance+) A normal Chest may be duplicated into a Red Chest or a Mimic Chest.
  • (except in Repentance and Repentance+) A duplicated trinket is mostly useless, as you cannot pick up two of the same trinket even with Collectible Mom's Purse icon.pngMom's Purse, Collectible Belly Button icon.pngBelly Button, or Collectible Smelter icon.pngSmelter.
  • (except in Repentance and Repentance+) In combination with a 48 Hour Energy pill and Paper ClipPaper Clip, the initial Locked Chests on ChestChest can be infinitely duplicated and opened.
  • (except in Repentance and Repentance+) In Greed Mode, if a Lil' Battery appears in the ShopShop and a 2 of Diamonds2 of Diamonds is acquired, infinite money can be gained by duplicating the Two of Diamonds.
  • (except in Repentance and Repentance+) By dropping a card, rune, or pill in a room with no other pickups, then using D1, this item can function similarly to Collectible Blank Card icon.pngBlank Card and Collectible Placebo icon.pngPlacebo.
    • (in Repentance and Repentance+) By dropping a card, pill, or trinket in a room with no other pickups, then using D1, this item can function similarly to Collectible Deck of Cards icon.pngDeck of Cards, Collectible Mom's Bottle of Pills icon.pngMom's Bottle of Pills, or Collectible Mom's Box icon.pngMom's Box (But without the luck up or doubled trinket effects).
  • (in Repentance and Repentance+) A duplicated card has a very rare chance to turn into a Dice ShardDice Shard, Cracked KeyCracked Key, or Emergency ContactEmergency Contact; however, these will always duplicate as themselves instead of duplicating as a card.
  • (in Repentance and Repentance+) A duplicated Gold Pill will turn into a random Pill chosen from the Pill Pool.
  • When duplicating any type of chest, the contents of the original chest will be invisibly rerolled.

Synergies

  • (in Repentance and Repentance+)Collectible Book of Virtues icon.pngBook of Virtues: Spawns a white six-sided die wisp on the middle ring. An extra wisp spawns if no pickups are duplicated.
  • (in Repentance and Repentance+) Character Tainted Lost icon.pngTainted Lost: Duplicated cards have an increased chance to be Holy Cards.

Interactions

  • (in Repentance and Repentance+)Collectible Guppy's Eye icon.pngGuppy's Eye: Guppy's Eye can be used to see what changed when duplicating a chest. It will not immediately show the new contents, but leaving the room and returning will reveal the changes. This essentially allows rerolling the rewards within them, especially useful in ChestChest and Dark RoomDark Room.

In-game Footage

Trivia

  • (except in Repentance and Repentance+) D1 is the only die item that doesn't re-roll anything.
    • (in Repentance and Repentance+) The D1 now creates randomized pickups, meaning that the description is more accurate to the item's effect.
    • (in Repentance and Repentance+) As an exception, Collectible Spindown Dice icon.pngSpindown Dice and Collectible D10 icon.pngD10, although they technically do re-roll items/enemies, have a controlled and consistent result.
  • D1 is the only standard die item that doesn't have the respective number of sides as outcomes, but rather, just a D6 with all sides having singular pips. Rather, an actual D1 would be more accurately pictured as a Mobius strip, a sphere or an actual real-word “denary die” similar in form to a cyllindric object with slanted top and bottom.