Last month Nintendo confirmed that they would be releasing their first smartphone game next year in March. At the time, the only information Nintendo was willing to release was the release window, but an earnings briefing attended by The Wall Street Journal revealed that all of Nintendo's smartphone games would be free-to-play.
"Games currently in the pipeline are all free to play," DeNA CEO Isao Moriyasu said. We had known that Nintendo's first game, Miitomo, had been confirmed to be free previously, but the remaining games in Nintendo's pipeline had been in the grey zone.
While the games will be free-to-play, they will feature the option to buy in-game items. The monetization will be decided "based on user expectation and gameplay." As far as what kind of games Nintendo plans to release before March 2017, they are considering all of their major franchises. So, maybe we will be seeing a new Metroid on mobile…