Nintendo does not offer for sale, sell or distribute its games digitally other than from Nintendo's eShop platform.
If you see games offered for download using Peer-to-Peer networks, or by clicking on links to files hosted on third-party platforms, the content that you are accessing is an unauthorised copy (i.e. a pirate copy). Pirate copies of game files are often referred to as “ROMs”.
The uploading and downloading of pirate copies of Nintendo games is illegal.