The Shield of Asgard is a mystical in Uncharted 4 multiplayer. It is the new mystical that came with Patch 1.13 (AKA: The Bounty Hunters DLC). With the Shield of Asgard activated (via L1 + R1 after being purchased from the in-game store), your health is increased by 75%, but you move 50% slower. You can only purchase this mystical (to use in-game) either through a DLC weapon chest (costing 4000 Relics) or for 600 Uncharted points.