The Hero xp system sucks your highly relying on spending crystals tried grinding xp it wont do much and it sucks that you have to go online just to claim things and half my crystals I just spend them on gems for a new hero and not for xp exchange what even more sucks the 2nd tower upgrade are locked by buying through crystals and the only way to get crystals is by going online and claim it from the mine not all ppl has internet connection for that same goes to gettinf runes upgrading them