Doubloons are special items that grant powers you can use in combat. Doubloons are primarily received as loot from multiplayer chests (treasure that requires multiple Pirates to open). Once you own Doubloons, you can open your Doubloons page and sort them, like powers. Doubloons closer to the top of the list have a greater chance of appearing during combat.
During combat, you can choose from one or more Doubloons at a time, depending on how many players are in combat with you. You can choose to use it or discard it. Once you use it, it’s gone!