
Normal rooms will not show the red outline if they are at the map's boundary.
The I AM ERROR room door can only be created while already inside a Red Room. Additionally, this doesn't work during Red Redemption (challenge #44). No door outlines will appear at any boundary walls. This does not occur in Corpse II, Dark Room, Chest, The Void, or the special version of Mausoleum / Gehenna II containing Dad's Note. The starting room of a floor is always in the center of the 13x13 area. If a door created by Red Key takes Isaac outside of the 13x13 area of the floor, he will be taken to the I AM ERROR room. This can also be done by using a Cracked Key, which can be obtained through room drops or by leaving a trinket in a boss or item room and coming back to that room during the Ascent, and using it in the same spot.
If Inner Child has not been unlocked, the room will contain a Shopkeeper. If the respective Tainted character has already been found or a Tainted character is played, the room will contain Inner Child instead.This room will actually be a closet containing a non-tainted character's Tainted form.
In Home, Isaac can create a "Red Room" on the left side of the map right under Mom's room.
All rooms made by Red Key will be 1x1 rooms that can have doors available on all sides.