for all who just started playing who have trouble with the energy system, when killing people and those skull-things float up, hover your mouse over the skulls and you get extra money and you energy restores by a small amount.
wait, WHAT?!?!? NEW LEARN TO FLY!!!! AWESOME!!! AND WHATS THIS?!?!?!? AT THE END OF CLASSIC MODE IT SAID THAT THERE WILL BE LEARN TO FLY 3!!!!!!!!!!!!!!!!