Energy

Energy in knights and dragons doesn't govern every action, like it does in other games. Instead, it is used to restrict the amount of time you can spend fighting in the arena tournaments. To ensure that the leaderboards in each tournament come down to skill rather than the sheer number of times people can fight in them, you are limited to one battle in the arena per piece of Energy.

Because Energy is not used in regular tasks, once you knights' health reaches zero you will normally have at least a few pieces of Energy to use in the arena.

The maximum Energy is 5, but if you receive some as you do occasionally as Arena rewards, then you are able to add it onto those 5. Energy recharges over time, but if you are absolutely desperate to fight in the Arena, you can purchase it with gems. This obviously gives some Arena fighters a bit of an advantage, if they are willing to spend money to fight more frequently.