Creepy Crate
Source: World Event. Previous owners of the crate have reported the disappearance of other pets from their collection. Undead type. As part of Hallow's End, at the end of a chain or rewards you with which teaches you which summons this companion.
The 
Creepy Crate is a companion pet rewarded at the end of a Hallow's End quest chain, available only while that world event is active.
Guide awaiting review
Start the Quest Chain
During Hallow's End, pick up the quest Missing Heirlooms to begin the chain. The breadcrumb quest A Friend in Need can lead you to it but is optional.
Complete Horde Quest Chain
For Horde players, complete the following quests in order, all taking place in and around Orgrimmar with one stop in the Undercity: Missing Heirlooms, Fencing the Goods, Shopping Around, Taking Precautions, The Collector's Agent, and What Now?
Claim Your Creepy Crate
After completing the chain, the final quest The Creepy Crate (Horde) or The Creepy Crate (Alliance) rewards you with the item that teaches the Creepy Crate companion.
Tips
Creepy Crate is not cageable, meaning it cannot be traded or sold on the Auction House.
