Fire a burst at your feet while flipping backwards 15 meters. Casting again within 4 seconds increases the cost by 33%.
Vault is a Scribed skill Grimoire, on the Bow skill line. It can be purchased after earning the Bow Master achievement from Chronicler Firandil in the The Scholarium once per character. It costs 0005000050,000 the first time, and 0001000010,000 for other characters on your account after that. The name of the scribed skill changes depending upon your choice of Focus Script.