Well, one can argue is that Mario and Luigi needed the help of a fire flower or a different power up to use different abilities. They learned abilities Fire/Thunder hand without the use of an item in Superstar Saga. But then as Koopaul said, one game.
I like the idea of a thunder ball instead of a fire ball because I'm thinking of this as more of an aesthetic change then a completely different move all together, but whatever, I'm cool with either way.
EDIT:
Oh right. Something came to mind for Roy. I've seen him do a critical hit in his game when he get his signature sword. Maybe it could be his B move? A powerful, slow sword swing. Just something I remembered.
I like the idea of a thunder ball instead of a fire ball because I'm thinking of this as more of an aesthetic change then a completely different move all together, but whatever, I'm cool with either way.
EDIT:
Oh right. Something came to mind for Roy. I've seen him do a critical hit in his game when he get his signature sword. Maybe it could be his B move? A powerful, slow sword swing. Just something I remembered.