Doors can be unlocked without using keys. Opening a door this way brings Isaac to an in-between room that resembles ???, with a few monsters.
Quote
"Look between the rooms"
Effects
- Entering a room that requires a key does not consume a key, but brings Isaac to a room resembling ???, which acts as an in-between of the two rooms.
- These rooms contain assortments of Blue Gapers, Blue Boils, and/or Blue Conjoined Fatties, and are always long rooms (either normal or slim). They have a chance to give a reward when cleared, like normal rooms.
- Doors that require two keys to open, such as Vaults or Dice rooms, will be opened instantly instead of waiting for the animation of both keys to be used.
- Once exited, the room cannot be re-entered.