I'm at third cave,Tin cave level 6,almost level 7.My upgrades for this specific one is level 3 Copper and level 6 Tin.For drops,I only have level 3 Stone and level 2 Tin.100 energy cost me 227MCC and get me only about 150-200 MCC so yeah,I have to wait each time a while before I can buy another one especially when broke.What do you think I have to upgrade to fix it?