Every single stage is full of lovingly rendered little details that are easy to miss. For instance, if you pause and zoom out on Mr. Game & Watch's stage, you can see you're fighting inside an actual Game & Watch console from the '80s.
Nintendo via GameXplain
The Game Theorists did the math, and taking into account all the variants and such, there are over 1 sedecillion possible matches in this game. That's a number with so many zeros that if we tried to type it out here, it'd probably break the website, if not the Universe. Of course, we're just going to keep playing as Yoshi and poop opponents off ledges, but it's cool to know we have options.