During Nintendo's third investor's meeting the company had hinted at what fans can expect from the second mobile game. According to The Wall Street Journal. Nintendo's rate unfortunately had a sharp drop in their net profits, but despite that we had some good news during the meeting with the announcement of Nintendo's second mobile title featuring one of Nintendo's major IP.
However I am surprised that they're now talking about the second title, when we haven't really heard news on Nintendo's first mobile title Miitomo, perhaps we'll hear more on that in a future direct, which I'm surprised we have not received one just yet.
As for which character they'll use for their second title I believe it will probably be Mario, because if they do plan on doing something for Zelda it would be probably one of there future titles, and the reason for why is because not only is this the 30th anniversary for Zelda, but back last year in April there was an April Fool's prank for a future Zelda mobile game working with the game, and I think there is some truth to that. I think it would work. It wouldn't have to be big, but just enough to where it want you to play more of it. As it said they wanted to use the mobile games as way to get gamers to play those games.
Also we already have Pokemon Go do that rules Pokemon out. The only other characters I can think of that would work would be either Samus, Donkey Kong, or Kirby, because those characters if the game is done right then it probably work.
So that's it for now. There really isn't that much more to talk about except possible speculation of what that second game could be. I'll be sure to talk more about this as soon as I have more information.