Had this idea for a while now, and I'm not sure if somebody's already discussed it, but what if you could get energy as a drop? Perhaps a little less rare than Orbs and more rare than Fire Crystals, but you could get small amounts of energy dropped from treasure boxes.
It would be in increments of 1 or 2 energy per drop, with rare drops of 5 and super rare drops of 10. They wouldn't come in three's like rarities, but it'd be a slow way of accumulating energy without spending crowns. Thoughts?