Demons: WoW Battle Pets
Select a pet:

Vendor: Falara Nightsong
Zone: Thaldraszus
Drop: Box of Collapsed Reality
Approximate Drop Rate: Unknown

Promotion: SteelSeries x World of Warcraft 20th Anniversary Celebration
TIP: When you browse pets by family, not all pets include an item. Those that do not are typically wild pets obtained through pet battling.