So the mirror universe is somehow strangely connected to the regular Star Trek universe where they have mostly evil versions of the good guys, which is virtually impossible since both universes have such different histories and circumstances. But despite that as I said both universes are strangely pegged to each other.
But it's also established in other episodes that there are an infinite number of alternate universes. So I take it all the other universes with the good guys have an endless number of evil mirror universes to match each one.
But it's also established in other episodes that there are an infinite number of alternate universes. So I take it all the other universes with the good guys have an endless number of evil mirror universes to match each one.