MMO-Champion datamined the upcoming beta build and found another pet!
Except... this pet isn't available to players and is technically not new. Terky was part of an iCoke promotion waaaay back when WoW was in vanilla. It's no longer available.
My guess is that developers had to add this pet in and tag it as a battle pet for the (few) players that actually managed to snag this companion. It sits in the same boat as other discontinued pets, such as the Onyx Panther. Even though we can't obtain them anymore, they still need to exist in the Pet Journal for those that do happen to have them in their collection.
So it's unfortunate, but Terky is just a tease for most collectors. :(
It's a shame that the majority of players still don't have access to a standard (non-clothed or themed) baby murloc pet (of any color), without having to shell out hundreds if not thousands of dollars.
UPDATE: After a bit more digging, a few players are saying that this pet and the promotional quest that rewards it was never really meant to be completed. Yes, it was an iCoke promotion, but it was only considered and fell through in the end.
So it was implemented, but Blizzard changed their mind and decided to make the pet unavailable to players. However, before the quest and companion could be removed from the game, someone picked it up and shared it with everyone else.
I can't verify any of this information, but this makes sense.
What doesn't make sense is why Blizzard would reintroduce Terky as a battle pet. Is there hope for pet collectors that an originally skinned baby murloc might be readily available in the near future?
Or it really is just a teaser. :(
UPDATE #2: The Pet Journal says its source is from an iCoke Taiwan promotion. So much like many other promotional pets, this was region specific.