This toy is sort of a sister toy to the Magic Pet Mirror, except instead of turning you into your pet, you turn your pet INTO YOU. How freaking awesome is that?
After some testing on Alpha, here's how it works. Keep in mind that all of this is subject to change, nothing is set in stone yet!
Toy has a 1 hour cooldown on it.
Your targeted pet receives a buff (unlimited duration, but disappears when pet is unsummoned) that transforms it into whatever your character looks like.
This transformation stacks with other buffs such as the Magical Mini-Treat and Magical Pet Biscuit.
You can transform pets that naturally hover and they'll continue doing so even when they look like you. Pets that fly alongside your character also continue to fly.
The effect works on all types of costumes/transformations, including druid shapeshifts and temporary costumes (tuskarr costume in the image above is the Underbelly Elixir from Northrend Dalaran).
Basically, if YOU can look like something so can your pet (temporarily)!
Shapeshifting out doesn't remove the effect from your pet. Likewise, changing your gear doesn't cause your pet to change gear. Whatever you looked like when you used the mirror on your pet, is what your pet will look like for the duration of the buff.
Pets retain their idle animations while transformed into your character. Cats continue to sit and sleep, for example.
On top of that, pets continue to perform their normal interactions. Emoting sit to your feline pet that's transformed into you causes some...interesting results. XD
And just for fun, some other interactions while under the effects of Narcissa's Mirror. I don't have access to my full army of pets, so I can't test them all. But I'm going to guess that all pets that have an interaction will continue to perform them even while transformed.
Unborn Val'kyr disguised as me resurrecting a dead critter.
Grommloc disguised as me roaring and fearing nearby critters.
Other things to note: Character special effects such as Shadow Priest's Void Form does not transfer over to your pet. I think for the mirror to count it as a costume it has to be an actual model change. I'm unsure about buffs like Pepe, but I have a feeling they won't copy over.
Also, pets with Narcissa's Mirror buff don't keep the costume while in a pet battle; they revert back to their original form when fighting.
I absolutely CAN'T WAIT for this toy, and I'm very eager to discover where it comes from. Quest? Achievement? Vendor? It might make for a very nice Pet Charm currency dump...*cough* ;)
With so many possible transformations, I feel like this toy may get some nerfs and/or restrictions in the future. I mean, is Blizzard really ok with all of the possible (temporary) pets that we'll come up with? While I'd like to hope so, part of me isn't sure the answer is 'yes'.
But with all things Alpha/Beta, we'll see. Things can and will change.
Regardless, I'm ecstatic that they're adding this toy in Legion. It may very well replace my current favorite toy (Magic Pet Mirror lol). XD