The three ironclad rules of the Mirror World:
First, everything in the Mirror World is the opposite of the real world, except for copies.
Second, the Mirror World duplicates everyone and everything that enters it, and the copies have the same or similar traits as the originals.
Third, the longer you stay in the Mirror World, the more closely your copy resembles you, until it becomes identical. So if a copy appears in the Mirror World, kill it as soon as possible.