What happens when I tap on the Energy icon?

When you tap the Energy icon shown at the top of most menus, you will be shown the Get Energy screen. This screen provides a couple of options for you to regain Energy.

You can either spend 99 Gold to completely refill your Energy bar, or you can watch an advert to gain 2 energy.

Note that you will also be taken to the Get Energy screen when you try to start a Mission when you don't have enough Energy.