I recommend adding an increased powder upgrade. Each shot would cost X amount of $, mabey 5$ per powder used. The upgrade will probably be cheaper because it increases the powder you use. It would act similar to the power upgrade but make a cost per shot. There should also be a material system. Possibly this could work by having purchasable cannonballs that would affect only one of your multishot balls. Ex. a feather ball to make one lighter, or a flat ball that could be more aerodynamic and bounce more but have more friction. Thankyou for providing such an amazing game to the community for free!