Puzzle Breakers is designed to ensure players have the chance to play various game modes, so if you're out of World Energy, you can still raid other players' Kingdoms or attack a Giant. Please note that the game is balanced to ensure your energies are fully replenished every few hours, but players who don't want to wait can purchase Energy points with Gems.
More ways to get extra energy may be introduced in future updates, so please stay tuned.