Deathwatch Hatchling
Sold by Challenge Warlords: Gold - Guild Edition. This hatchling has an unusual sense that allows it to detect and follow along with alpha predators. Beast type. This Pet is a reward from and is sold by the Guild Vendor.
The 
Deathwatch Hatchling is purchased from a Guild Vendor for 
300 Gold, but requires completing the Challenge Warlords: Gold - Guild Edition guild achievement and reaching Revered reputation with the guild.
Guide awaiting review
Join a qualifying guild
Find a guild that has completed Challenge Warlords: Gold - Guild Edition by visiting guildsofwow.com, filtering by region, realm, and faction, then sorting by Achievement Rewards to find guilds with that achievement. Known active options include Menace to Sobriety on NA-Area52 (apply through the in-game Guild Finder) and Nephilim on EU-Silvermoon Alliance (contact Ash#2557 on Battle.net or ashelia_87 on Discord for an invite).
Reach Revered reputation, then buy
Earn Revered reputation with the guild, then purchase the Deathwatch Hatchling from the Guild Vendor for 300 Gold (which may be reduced based on your guild reputation level). The pet can also be caged and sold on the Auction House if you prefer to obtain it that way.
Tips
If you cannot find a qualifying guild on your own server, creating a character on another server to join a guild there, buying and caging the pet, then selling it back on your home server is a viable option.
