|Explore the other side|
|Defeat The Witness as Cain.|
Red Key is an unlockable active item.
- While held, a red outline of a door will appear on walls which a Red Key can be used on.
- Approaching one of these outlines and activating the item creates a door that leads to a red room.
- The red room can be several types of rooms, including but not limited to:
- You cannot use the item unless you are close to an outline.
- In rooms with multiple outlines, it only opens the closest one.
- A red room can be created through another red room.
- The red rooms have a physical presence on the floor unlike Devil Rooms or I AM ERROR rooms and can be re-entered at any time.
- Red rooms follow secret room rules, meaning that all other rooms it connects to must have clear space for a door to the red room.
- As a result, all red rooms are symmetrical, and if there's enough space you create a large area of red rooms.
- Although a red room can be adjacent to more than one room if the room type is one that requires something like a key, each entrance to the room will have its lock.
- You cannot build a red room outside the boundary of the map. Trying to do so will open a door which leads to the I AM ERROR room instead, which you cannot return from.
- You can tell if a red door will lead to an I AM ERROR room if it does not show up on the map.
- The max boundary size of a map is 13x13 rooms.
- The max number of rooms in a single floor is 128, counting all the rooms of the original map (including Secret Room and Super Secret Room, also double and quadruple-sized rooms count as one) plus the rooms created. After the count of 128 rooms, the Red Key will not open new doors and the charge is wasted.
- Red rooms can be special rooms even in The Womb / Utero / Corpse, Sheol, Cathedral, Dark Room and The Chest, where these types of rooms otherwise would not be generated.
- You can create I AM ERROR rooms on the Chest indefinitely, allowing you to restart the chest until the game inevitably crashes.
- Special Red Rooms are unique from the regular rooms of a floor (meaning that a Red Room shop will have its stock separate from the floor's regular shop.
- Item Rooms generated with the Red Key will only have one item pedestal, even on the Antibirth floors.
- Red rooms cannot be opened using Dad's Key.
- Red Rooms can be used to connect the Primary and Secondary areas of the Mausoleum to one another.
- Entering an I AM ERROR room while in Sheol will take you to the Dark Room, even if you do not have the Negative.
JABM M6NE - Curse room next to spawn
T26E CR6B - Curse room next to spawn
9J99 2YMW- Curse room next to spawn
2ZX3 XKBQ - First-floor curse room
8EMD 1ASP - First-floor curse room
BZP1 7KLB - First-floor curse room
9FTC V9SK - Right red chest in first-floor curse room, if rerolled twice
2VPF Q402 - Eden spawns with this item.
9B6C 8TWY - Curse room next to spawn
78WE 8GWS - First-floor secret room, below spawn.
RNJL KHXY - Curse room next to spawn, re-roll the goat head into it.
- This item may be a reference to red rooms. Red rooms are an internet urban legend originating from the Deep Web, allegedly being hidden websites or services where viewers may pay money to torture or kill innocent victims.
- This item may be a reference to the item of the same name in the RPGMaker Game LISA: The First, in which it is used to access a red basement.
- In Repentance, this item's unlock method was changed to reaching Home and opening the chest in Mom's room. It is also vital for unlocked the Tainted characters. Its original unlock method is referenced by Soul of Cain, which allows for a single-use Red Key effect on every available door.