Wolpertinger's Tankard

Wolpertinger's Tankard summons and dismisses Wolpertinger, a wolpertinger companion that follows you around.

Source
On US servers, Wolpertinger's Tankard is a quest reward from, part of the Brewfest seasonal event.

On European servers, the quest is not available and Wolpertinger's Tankard can be purchased from Token Redeemers and Brew of the Month Club vendors. It is available for purchase only during Brewfest.