I was watching a special on the Tungusku Explosion and theories of its origin. One of the scientists held that an incursion of "mirror matter" caused this event. I have never heard of mirror matter before. Is it like anti-matter? Is there dark mirror matter? If we substitute "mirror mass" in Einstein's equation, do we get "mirror energy". Would that be the same as "dark energy"?

Yes, Tungusku really happened. It is not just a joke in Ghostbusters.
Yes, Gene Rodenberry did not invent Anti-matter.