Nintendo is nowhere near as bad to fan projects as people say they are. with the exception of Pixelmon and Mario Bros. X, which both had concepts similar to games they were about to announce at the time, they've only taken down projects that are funded/monetised by ads or crowdfunding; and/or are remakes. not justifying this action in the case of the prior, but it's probably safe to make a fangame as long as it's not a remake or Patreon-funded.