
It looks fantastic, and it seems to be using the Tyrael's Hilt pet skeleton. (It's not a downsized Valkyr model as you can see. Stoked!
Also: a robot model that may or may not be a new pet:

Raiding with Leashes II: Attunement Edition (New)
So, 5.3 brings new raid drop minipets, something I personally have been waiting for. Sadly, it's not quite what I'd hoped.
I don't mean to sound ungrateful, but a lot of those pets are recoloured versions of currently available minipets, which makes me a bit sad. But still, it's better than nothing.
(I really hoped for a Mini Lurker Below though.

[Coilfang Stalker] drops from: very likely Lady Vashj
[Lesser Voidcaller] drops from: High Astromancer Solarian
[Lil' Bad Wolf] drops from: very likely the Big Bad Wolf/Opera Event
[Menagerie Custodian] drops from: very likely The Curator
[Netherspace Abyssal] drops from: very likely Prince Malchezaar
[Phoenix Hawk Hatchling] drops from: very likely Kael'thas
[Pocket Reaver] drops from: very likely Void Reaver
[Tainted Waveling] drops from: very likely Hydross the Unstable
[Tideskipper] drops from: not sure, I think it might drop from Morogrim Tidewalker and look like him.
[Fiendish Imp] drops from: very likely Terestian Illhoof
Reward for collecting all: [Tito]
Aside from that, there are a few other pets, including one that might either excite you very much, or make you feel a bit sad but also happy. I'm sure you'll know when you see it.
Miscellaneous 5.3 pets:
[Direhorn Runt] rewarded by: [Brutal Pet Brawler]

[Gahz'rooki] rewarded by/drops from: unknown, presumably Gahz'rilla
[Viscous Horror] rewarded by: unknown
[Filthling] rewarded by: unknown