Arena Grand Master

Arena Grand Master is a rare quality trinket that gives a passive stamina bonus and a damage absorbing shield.

Source
Arena Grand Master is the reward from the quest Arena Grandmaster that starts from the Arena Master trinket lootable from the chest in the Gurubashi Arena. You must collect 12 trinkets to form the Arena Grand Master. The chest only spawns once every three hours during the Gurubashi Arena Booty Run.