Hypothesis: The mirror (or the whole room) connects universes. More specifically, there is only one mirror, stable in the multiverse (quantum, mathematical, magical or whatever) of compatible universes. A compatible universe is such an universe where the mirror exists, i.e. most probably the one that did not branch off before the end of Atlantis (or boltzmanned into existence a moment ago).

Looking into the reflection, your (magical) brain picks the image from a different universe, the one that matches your CEV most closely.

Nothing can hurt the mirror, unless the measure of the universes the action is performed in is a "significant portion" of the multiverse - otherwise it just dissipates.

The map shows gibberish, because, well, there is everybody and nobody in the last room...