The Mirrored World is an area of the 
Downpour II and 
Dross II. It is necessary to obtaining 
Knife Piece 1. The layout of The Mirrored World is the exact same as the normal floor except mirrored horizontally. Each room contains the same enemy encounters and has the same block layout, although some rocks may be bomb rocks or X rocks in one world but not the other. The boss is also identical, and, if defeated, will drop a second randomized item from the Boss item pool.
Accessing the Mirrored World
In Downpour II or Dross II, there will be a room with a mirror on the side of a wall. In another part of the map, there will be an inextinguishable white fire. Coming into contact with the fire will turn the character into The Lost. After turning into The Lost, walking into the mirror will grant access to the mirrored world.
Notes
- The floor's appearance will take on an otherworldly appearance. Additionally, any items will have their artwork inverted, and the level's soundtrack is played backwards.
- Breaking the mirror is possible with a bomb, but it's not recommended as it will cut off access to The Mirrored World.
- Breaking the mirror while inside the mirrored world will cut access from the normal world, and also will eventually cause Isaac to take damage and die.
- Items, Pickups, Monsters, and UI are also mirrored
- The Item in the Treasure Room will always be replaced with
Knife Piece 1.
- On XL floors, no items will spawn in the second Treasure Room. However, both Boss Rooms will contain a treasure as normal.
- All secret and ultra secret rooms will be empty, as will the shop's inventory. There will be shopkeepers, however, which can drop items as normal.
- Trapdoors will not be spawned, except to crawlspaces – which will have no items.
- Wraiths will appear visible, but they will lack reflections unlike other entities, opposite of their normal appearance.
- The rooms in the Mirrored World count as separate rooms, so anything that happens in the normal world room will not affect the mirror world variant of the room.
- If you start the game as The Lost, you can walk through the mirror without the help of a white fire.
- Tainted Jacob can enter the mirror if he has been touched by Dark Esau.
- The Tainted Soul can also enter the mirror without a white fire, and in turn, keep his health bar.
- The mirror can even be entered by throwing the Tainted Forgotten at the mirror.
- Even though Tainted Soul can enter the mirror, The Soul cannot.
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- The boss in the mirrored Boss Room is the same one as the normal world. Beating it will spawn an item from the Boss Pool; but, as it is only a mirror of the real Boss Room, no trapdoor, no angel room door and no devil room door will appear and the Red Key will work here.
- If a Planetarium Room exists on the on the normal world, it will exist on the mirrored world and require a key to open, even if you opened it on the normal world. However, there will be no item.
- To turn back into your original character you need to clear 1 room as the lost. If you are in the Mirrored world you will turn back after going through the mirror. If there are no rooms left on the current floor you can clear a room on the next floor and turn back.