Energy is an ability resource similar to Mana and Rage. Unlike Mana, a Hero's maximum Energy cannot be increased by leveling up or purchasing items - it is a constant value of 200. This is countered by Energy's quick regeneration speed (10/s), providing players with a steady supply of Energy to spend.
Players can still momentarily deplete a Hero's Energy pool, however, so they must time their ability usage carefully. Many Energy based Heroes have abilities that can restore Energy, allowing players to better manage the drain on their resources.
Energy is represented by a yellow resource bar instead of blue.