Maybe I was a bit extreme, but that's counting, of course, Mario Party games, Mario sports games, and any games involving Mario as a playable or important character. There are undoubtedly at least fifty.
As for Zelda games, I can think of. . . 9 that have already been released. And I think there may be a GBA game. . . and of course there's SSB, two more games (though Samus is also in those), and the three upcoming games. That's up to fifteen, which is certainly nearing twenty.