Adrenaline Urn is an item that is earned through the 2018 Halloween Event after 6 consecutive days of doing the event. Players can equip the Urn in the pocket slot, and it will start storing adrenaline during combat.
Once the Adrenaline Bar has reached 100%, all excess Adrenaline will be transferred into the Urn until filled. Once filled the following message will appear in the chat.
The Adrenaline Urn is now full.
The Adrenaline Urn can be stopped from depleting the Adrenaline stored if stalling with abilities or it can indefinitely stored if using an ability like Regenerate that would deplete the Adrenaline Bar to 0%.