I had a Blizzard Authenticator attached to my account from my Diablo 3 days, so I didn't even have to do anything to get my Core Hound Pup. Now he's running around the Eastern Kingdoms with me as I level (dinged 42 last night, almost "halfway" to 90!)
This guy can be used as a battle pet, but I haven't dove into that system yet, so I'll have to reserve judgement on his battle skills. He looks pretty viscous though...
Check out my Core Hound Pup Guide on Hubpages here.