My Little Pony: Friendship is Magic - That's And interesting Fact.

So in the mirror universe, Luna was actually good until she succumbed to the dark side. That's like the opposite of real Luna; real Luna becomes evil and turns into Nightmare Moon, is banished for 1000 years, comes back, is defeated, and turns good again.

That makes a lot of sense now….

"There could be a Sombra here too,"

So wait, they don't know about the Crystal Empire at this point?