Dr Mario, lucina and pittoo are extra bonus characters. They were intended to be skins buy sakurai thought that it would be cool to have them as their own characters. I'm not mad about their inclusion, of course I would rather have more different movesets on lucina and pittoo, but since it's like extra credit I'm not mad either. The only character I don't really agree with is corrin, too much fire emblem representation IMO, but as for shulk I like that