I think Bandana Dee from the Kirby series would be a great addition to the mix, seeing how he is also a main character, along with King DeDeDe, and Meta Knight. While he may not have many basic attacks, seeing how he only own a spear, he could work in ways similar to DeDeDe as well. In a smash fan game, Super Smash Flash 2, Bandanna Dee is a playable character, but what I found interesting was that, he also had the Beam Ability, and Parasol Ability, like Parasol Waddle Dees and Waddle Doos. They could add that into the mix as well, giving him his own Smash ability, like Kirby, which is unlikely, but possible. As a Final Smash, I could see him calling a swarm of waddle dee to attack fighters on the ground, and knock them into a combo made by Bandana Dee, a Waddle Doo, and Parasol Waddle Dee.