I saw a hunter with this pet a few minutes ago. Sorry for the shitty SS's but I just took them as quick as I could when I saw him in case he mounted up or something. Btw I asked him and he never answered so that's why I'm asking here.
I've never seen one of those before and I check wowhead but couldn't find that model.
Edit: I forgot I found one of wowhead *Svarnos* which is in Tol Barad but there is no screen shot of that one so it could be it.
It's a Core Hound just a new one u can tame from the blackwing lair raid.. some bosses in, but u'll need 2 more players to help u get it.. since u have to be 3 people at first boss
Like others have said. It's Chromaggus from Blackwing Lair. He's the boss right before Nefarian. Before this latest patch, he was considered a dragon, and not tameable (he's a core hound mixed with dragon dna). But, for some reason, they decided to make him a beast, thus tameable. I helped get a hunter in my guild this pet. Puts my Molten Core core hound to shame