A hero has two important types of energy they must manage in order to join in battle: Constitution and Fortitude. The stores of Constitution and Energy stored up by a player can be found next to their name in the top left corner in the Home City. Both Constitution and Fortitude restore one point every 8 minutes.
Constitution is consumed in order to enter into a level. Each level has its own value of Constitution that must be used in order to complete it. Constitution can be recovered by consuming Constitution Pills, or by joining in Feasts during certain times of day.
Fortitude is consumed in order to engage in PvP. This includes Pickpocketing, the Arena, 3v3 Battlefields and the Real-time Arena. Fortitude can be regained by consuming Fortitude Pills or can be sent to you by your friends and can be received from your Mail.