Sometimes when Pill with Telepills effect is used, it can teleport character to the mysterious Error Room. Error rooms can also be obtained by any other means of teleportation, like with the items undefined or teleport. Every Error Room is different, and can have items for free or for sale. They can also contain trinkets or consumables. Getting an error room in the dark room or the chest makes it to where you can redo the floor.

Binding of Isaac Rebirth 2014-11-29 13-24-49