My first suggestion is decrease the cost energy of dungeons or increase the amount of crystal gems that we can get from in game content. The reason is, let the players keep playing the game is the best way keep your customers. I believe there r 2 different types players in game. They first type is people who have money but they don't have a lot of time. These players like to make their characters become stronger by purchasing in game items. The other type of players are "poor" players. They have time but they don't have that much money for purchase items. It doesn't means they never purchase items.  Unfortunately, the fact telling us even players purchase items they still taking too much time to make their characters strong.  Players who wants to pay their time for making their characters strong will never come true, because they are out of energy. This is ridiculous. This is how you lost your customers. My second suggestion is, sending energy rewards to players mail boxes instead of charge them directly.  That's all!