For a long while now, Nintendo has been giving some of their upcoming first-party releases a trailer that gives a general explanation of the game. These overview trailers are usually uploaded in Japanese first, and then an English version releases a few weeks later. This isn’t limited to new games either. Although it doesn’t happen as often, Nintendo will sometimes do this with DLC releases as well.
For example, Nintendo has released a Japanese overview trailer of the first wave of the Mario Kart 8 Deluxe “Booster Course Pass” DLC. That said, Nintendo did stray from the usual pattern with overview trailers by releasing this one at the very last minute. Nevertheless, if you want to get one last look at gameplay of the new courses before you play them yourself, you can see the trailer down below.