Core Hound Chain

The Core Hound Chain teaches you the Core Hound mount, and was originally a special anniversary event award.



Source
It can rarely be listed on the Black Market Auction House by Majordomo Executus, for the opening bid of.

This item was awarded by the achievement Boldly, You Sought the Power of Ragnaros during WoW's 10th Anniversary event.

It is sent to your mailbox by the WoW Dev Team upon completion:

Mount Journal
Molten to the core!