I want a new final Smash for Mario. Hear me out.
Get a Smash Ball. You press B, and Cappy's eyes appear on Mario's hat. Now he has one shot to throw him, with the potential to miss. If you connect with another player though, Mario gets sucked into that character's body, using the same animation as Odyssey. (Visually, in mario's place, a small flag appears. It is strictly for animation purposes.)
Once Mario has captured an opponent (they, of course, have cappy on their head, blue eyes, and Mario's mustache), he has free reign to do what he wants with them for 30 seconds. He can use literally any of their abilities to fight other opponents, if he chooses. He can also choose to jump off a ledge.
If the character Mario is controlling dies, or the 30 second limit is up, Cappy flies back to the flagpole, and swings around it, while Mario poofs back into place, using the same animations as fast-travel in Odyssey.
This sounds absolutely too perfect to me, and suits Mario a hell of a lot more than firing a giant fireball.