Core Hound Pup



The Core Hound Pup is a core hound companion.

Source
This item is mailed out to all characters on accounts that have a Blizzard Authenticator or Blizzard Mobile Authenticator attached, including accounts that are attached to an authenticator in the future. It represents the authenticator as being the "guard dog" of your account.

Pet Journal
Found in the Firelands and the Molten Core, core hounds can trace their lineage back to the alpha male, Magmadar.

Letter
Players are mailed this companion by the WoW Dev Team:

Previously the pup was sent from Breanni with the letter: