Just speculation however it seems that the Switch version of Mario Kart 8 is expected to come with additional features that the Wii U version does not have.
According to Nintendo Life, it seems that it has been spotted on the box cover art of the upcoming game that was leaked (and taken down) on EB Games Australia’s website that “Battle Mode” will be returning to the game. Mario Kart 8 did have some version of Battle Mode, but it seems that many did not quite like it as much as its predecessor.
We’re not sure what “All new” means, like whether or not it will be the return of the original Battle Mode or an improvement on the existing version. It was also revealed that gamers can look forward to a whopping 24 extra tracks, which means that there will be 6 more cups that gamers can race on. There will also be 10 new characters added to the game (with King Boo a pretty much cert to be one of them).
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Official news should come from Nintendo on Jan 12th. I used to love the original battle mode on the SNES. With more fleshing out it could be a very good enhancement to this game.