You can only compare the behaviors of the characters not the design.

@RIG  
facehoof They’re the same thing!

Makes me wonder what .mov Chrysalis would be like, if she was ever put into the series.

@Prof.NightJack  
Technically no, that’s just an AU (like EQG’ human world is)
 
I mean, there’s no hard definition or the like but all stories where mirror universe is used is when the personalities are flipped, good becomes evil, evil becomes good, and that’s not even firm.

Perhaps mirror universe are like the human world in Equestria girls,very similar but with one major difference from the get go(humans,alien invasion,my little cuttle fish) but often the inhabitants follow nearly the same path as the prime universe(or as close as their difference will allow)while alternate universe are the same universe but with a major deviation from the prime.An alternate will simply follow the primes timeline until the potential for difference is greatest creating new perspectives and factions(luna banished corona,Derpy element of loyalty,Rainbow dash becomes celstias student)if they still seem the same well then…I don’t know ,their all weird and stuff,it’s all a bunch alternative and extra-dimensional hoopla that will all seem as silly as people thinking their was civilization on the moon before we actually went their and found out.

i like to think there is a humanverse where everything is the same than the primeverse (magic, story, places) except for the fact that most of the characters are humans, unlike the other humanverse we have…

@Masem  
Yes, this is true.  
I wonder if a gender switched universe could count as a mirror universe under the right circumstances?

@Prof.NightJack  
More specifically, all mirror universes are alternate universes , but not all alternative universes are mirror ones. Mirror ones nearly always imply inverting the personalities of the characters; the .MOV series was more about exaggerating them

@RIG  
“mirror universe” is just a term often used for the dark/evil alternate universe, but it is an alternate universe as well, I’ve seen a few thing where a “mirror universe” is really just that, it’s all the same but left and right with switched.

And you point is?

nope, that is not a mirror universe, is an alternate universe.