Camilla from Fire Emblem
Purely biased pick. My vision of Camilla in smash is as a super heavyweight style fighter riding her Wyvern into battle.
Fire Emblem's Wyverns are quite large however, so scaling it down to fit in the game while still looking good may prove unfeasible.
Alternately she could just battle on foot like other fire emblem characters, but being a mounted unit offers a more unique identity as a character while also showcasing another aspect of Fire Emblem not yet represented in smash.
Camilla's default weapons in her original game are Axes and Magic Tomes. She lacks any unique signature weapons of her own, so she could use a variety of axe/tome weapons throughout the moveset, each with their own unique properties. Her Wyvern would obviously grant her multiple jumps too.
Being YET ANOTHER Fire Emblem character, while also being a "Waifu", plus her divisive nature within the fire emblem community itself, Camilla would probably go down as THE most controversial character reveal in Super Smash Bros. history, which I personally think would be absolutely hilarious to see unfold.