Batteries Not Included
Physical items in the real world can be used to cause changes in the game (e.g. Nintendo's "Amiibo"-figures)
So far, Nintendo has announced that any Amiibo from any game-series of a Smash Ultimate character will work with Ultimate. Sakurai mentioned that there won't be many new characters because of the effort on bringing every previous character into the new game, so there's question at the moment whether there will be character DLC.