A Strange Door

A Strange Door is a special exit that is unlocked by beating Mother for the first time. It leads to a special version of Mausoleum/Gehenna II, which contains Dad's Note, which starts the Ascent, and eventually Home and the fight against Dogma and The Beast.

The door spawns in the starting room of Depths/Necropolis/Dank Depths II. It can be opened by giving it The Polaroid or The Negative. This can be done through methods such as using a teleportation card, a Telepills, a teleport activated item, Ventricle Razor, or Forget Me Now after defeating Mom, escaping the boss room. The door can also be opened with Broken Padlock, Cracked Orb, Faded Polaroid, Soul of Cain, or Sharp Key, but not Mr. ME!, Dad's Key,Mysterious Paper, or a Get out of Jail Free Card.

Having more than one of The Polaroid or The Negative, (such as through Diplopia or R Key) will only remove one to open the door. Faded Polaroid is always taken first if held, then The Negative and then The Polaroid.

A Marked Skull always spawns somewhere in the second floor of the chapter. Destroying it will drop a guaranteed 0 - The Fool (or a Telepills if holding Little Baggy), giving a reliable way to open the door. It is recommended to visit the Boss Rush room for a free item before teleporting out if possible. The Telepills will become a ??? if Isaac has Little Baggy and False PHD, rendering it more difficult to exit the boss room.