Kirby Fighters first made its appearance in 2014 as a mini-game in the 3DS title Kirby: Triple Deluxe, and then as the enhanced standalone 3DS eShop title Kirby Fighters Deluxe. We didn't hear much about it until now as it seems a sequel will be released shortly. Indeed, on the official Play Nintendo website, a listing for Kirby FIghters 2 leaked, without any prior announcement. The listing, which is still available at the time of writing (see attached screenshots) reads the following:
Choose from a cast of Kirby’s most iconic copy abilities—including the brand-new Wrestler ability—and duke it out to be the last Kirby standing. Familiar friends and foes like Bandana Waddle Dee and King Dedede also make an appearance as playable characters in the Kirby Fighters 2 game, available exclusively for the Nintendo Switch system.
You can try to see the listing for yourself by going to the Game Finder for parents link on the Play Nintendo website, and under 'Which system do they play on?', select 'Nintendo Switch systems'. You will then find Kirby Fighters 2 as the second game.
Clicking on the listing however leads to an unavailable page (see second thumbnail above). According to this leak, Kirby Fighters 2 will launch exclusively on the Switch at $20.