If you are goint to port an existing game you definitely need to get permission from the copyright holders first. If you don't you risk being forced to shutdown

If you are goint to port an existing game you definitely need to get permission from the copyright holders first. If you don't you risk being forced to shutdown the project later, after already having spent a lot of effort on it. (This has happened to fan remakes more than once.) If you can't get permission, you're better off just taking the mechanics of the original game and making something based on those mechanics without using any of the original IP.