The Adrenaline Urn is an item obtained from the 2018 Hallowe'en 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 is filled to 100%, all excess Adrenaline will be transferred into the Urn. Once the urn has been filled, the following message will appear:
The Adrenaline Urn is now full.
The urn can be prevented from depleting by using abilities, and it can indefinitely stored if using an ability like Regenerate that would deplete the Adrenaline Bar to 0%.