DON'T DOWNLOAD THIS GAME! It's literally impossible to get through the event mines with all 20 keys without spending actual money unless you deprive yourself of sleep and spend every moment watching ads for extra resources. The developers even say not to do this, but if you want to beat it without paying money, you have to damage your health. The challenge is not in game play, but in staying conscious long enough to break rocks 20 levels higher than your goblins because balance... What's that?