Originally a side game in Kirby: Planet Robobot. 
"Power through bosses as a team of four! 
In pretty much the best team up ever, Kirby, Kirby, Kirby, and Kirby must unite to do battle in this free-to-start multiplayer action game! Choose from four roles to make your own Kirby crew, take on bosses, level up, and try out new challenges in this clash of power and puffiness. Are you a Sword Hero? Hammer Lord? Beam Mage? Or Doctor Healmore?! 
No matter what, each mighty role offers up a unique way to play. Puff up your power by crafting new weapons and spending materials at the shop to receive even MORE weapons, not to mention armor and items. Beyond the main game, there's also a ton of quests and a brand-new challenge system. Plus, tapping compatible amiibo figures/accessories will earn you extra fragments to help craft new gear! Are you ready? For Kirby, the answer is always fight and flight. "