I did some testing on the PTR using the Pet Mirror and found out some neat things.
- Any action performed (other than walking, running, and jumping) after using the Magic Pet Mirror will remove the effect.
- The costume can be Skymirrored and/or copied by other players.
- It has a one hour cooldown, and it applies a 10 minute buff.
- Stacks with other toys, but only if you use the other toys first and then the Pet Mirror.
- Stacks with Pepe on a few pets, but only if you apply Pepe first.
- Can't be used on pets that can't battle.
- You can perform certain emotes as the pet you mirrored!
The last part was the toughest to test. With a long cooldown and hundreds upon hundreds of pets to go through, it took a long time of cycling through characters to use their Pet Mirror (they don't share an account-wide cooldown on the PTR). I finally finished last night, though, and have a somewhat complete list of which Mirrored Pets have emote animations!
One thing to note about this list - Unfortunately I don't have an infinite amount of time to spend on the PTR testing each and every single pet for animations, so for pets that have the same or similar model (such as all the rabbits, cockroaches, etc.) I tested one and figured that any animations performed (or not performed) would also apply to the others that shared the same look.
So my list doesn't include EVERY pet (because, c'mon, that would be nuts), but it should cover all of the pet models.
Another point I should make - I didn't try out every single emote, just the main ones. Certain pets that are based on player-character models will probably be able to do all of the emote animations that players have.
I took some example screenshots for each tested pet (didn't capture all animations), but since there are over 70 images I'm only including the ones that I found the most interesting in this blog post. If you're interested in taking a look at all of the screenshots, I've created a gallery here.
Anyway, the list is long but I've sorted it by pet families and in alphabetical order. Some Mirrored Pets don't have any emote animations, but I included them anyway because... well, silly reasons. ;)
Pandaren Water Spirit