They've also only been doing classic mode. It's possible that if there are those "final five" fighters, that they have a unique unlock criteria. We just have to wait and see when either leaker gets the final one unlocked
He unlocked Dr Mario and now there are Wario, Jigglypuff, Rob, and Lucina left.
Leaving 4 more spaces! Mewtwo, Ridley, Chorus Kids, and Impa or Mach Rider.