Best Buy has recently listed Super Mario 3D World for the Nintendo Switch on their website, and this is already making some fans of the game excited. However, it would still be wise not to get your hopes high just yet, since this doesn't confirm, in any way, that the game actually exists.
Now, here's the thing: Best Buy has previously listed games like Metroid Prime Trilogy and The Legend of Zelda: A Link to the Past, and none of these games have been announced by Nintendo as of yet; considering that the listing popped up in April of last year, it is fair to say that they weren't real.
The difference between a Metroid Prime Trilogy, or even The legend of Zelda: A Link to the Past, and Super Mario 3D World, is that Nintendo has been porting pretty much every title in the failed Wii U's library; Super Mario 3D World is one of the few games left to be ported.
Super Mario 3D World was released in November of 2013, a whole year after the Wii U launched, and it was well-received in spite of it not being a new Super Mario Galaxy or a brand-new 3D game. Over the years, the game has become a beloved classic, and fans really want Nintendo to port it to the Switch.
Again, the game showing up on Best Buy's listing may not mean much, but Super Mario 3D World is the one game that could actually be announced for the Nintendo Switch rather sooner than later. We'll keep our fingers crossed.