Ill show you an example of how this could perfectly work: When you defeat Flameheartz fleet, you can find some deposit boxes with ghost balls inside, can't you? The normal ghost balls are a green ghost with the same effect of a normal cannon ball, the big ghost gives a lot of holes like a keg, and the red ghost is a fire one, so, I was thinking: What if Rare added customizable cannon balls for sale? They would have the same damage as normal cannonballs , the only difference would be their skin, they could even sell it at Pirate Emporium, it would be a way to give more profit to Rare, imagine if you buy a Bat Ball customization, so every time you fire your cannons, a Bat is shoot to the enemy ship, . Or What about a Pirate Legend customizable cannonball? Everytime you shot a cannonball, a Blue Skull comes from your cannon and hits the enemy ship with the same damage as normal balls?
Note: Im suggesting only new skins for cannon balls, im not suggesting to sell balls that give more damage like the Big Ghost balls from Flameheartz Fleet
Hope you like my suggestion
