There should be a Paper MarioTCG

A trading card game could definately work for this series, the same way they did Pokemon cards. They can have every fightable species as battle cards, with additional item cards, badge cards and maybe Magic cards (like one of Merlin's sisters powering up your battle cards). I'm not sure how the bosses would work though, especially like Shadow Queen and Bonetail. I guess you can do the same thing they did with legendary Pokemon and God Cards (Yu-Gi-Oh) where there difficult to play and really rare. That will also do marketing so maybe they can do a forth game (they would market each other). Each battle card would have the same basic attacks/special attacks, hit points, defense, etc that they have in the games.