Stamina is your energy in the game. It replenishes itself given an amount of time.
There are 3 kinds of Stamina:
1. Mission Stamina, this can be found above your screen beside the Pirate Leader Avatar and your name. It recovers 1 point of stamina every 5 minutes. The limit increases as you level up your account.
2. Duel Stamina, is your stamina for your Duels. The amount of Duel Stamina you have is shown in the Duel Button. Your Duel stamina replenishes 1 point every 6 hours. You can increase your Duel Stamina by upgrading your Cannon in your Hideout
3. Grand Arena Stamina is what you use to battle in the Grand Arena. The current amount of Grand Arena Stamina points you have is also shown in the Duel battle once you have unlocked the Grand Arena. Your Grand Arena Stamina replenishes 1 point every 6 hours. Your Grand Arena Stamina limit is fixed at 5/5.
You can use Gems to fully restore your stamina or use a Stamina Recovery Item. Some stamina recovery items are available in the Tavern and Duel shop, it's also obtainable when completing a certain achievement in the game.