Oh, I know. I don't have Fire Emblem listed as one of my fandoms for no reason. I guess if you are going to show off Robin it would make sense to mention her while you are at it. It just kind of felt like they made an awfully big deal out of her in the trailer for her to just be an alt costume. I was expecting her to be an alt for Marth the first time they showed off alt costumes.
Costume? Even in melee alts were more than costumes.
Alts have similarities, but definately have different moves, specials, stats, and physics, and she will probably have a unique final smash as well.
Ganondorf is a cap falcon alt, but calling him a costume would be pretty disingenious.
The differences are already pretty apparant, and shes only shown seconds of gameplay and screens. She two hands her falchion pretty often, something marth would never do.... And her swordplay looks to be quite noticably faster than marths.
Wii fit trainer male/female are costumes, along with villagers, and the Robins.... But Lucina, definately not a costume.