Fleet Stag Mantle is statless cape droped by Spirit of Kurnous, endboss of Hunter's Vale. The cape transforms player into deer with speedbuff of 50 % for x minutes. The cape has reuse timer of 15 minutes. To use the cape, drag it into hotbar and equip it and click the cape in the hotbar.
The cape is obtainable currently only by Tier 1 players, as player cannot enter Hunter's Vale after gaining rank 16. During the live event The Wild Hunt the instance was available for all ranks.