If you are looking for top-tier arena combat or "io-style" experiences available as NSPs (eShop digital titles), 1. Brawlhalla (The "Gold Standard")
While there isn't a widely recognized official game titled exactly on the Nintendo Switch eShop, the "io" genre is incredibly popular on the platform. These games are known for their "easy to learn, hard to master" competitive multiplayer loops. Brawl.io Switch NSP (eShop)
While not strictly an "io" game, it captures the one-hit-kill, fast-respawn chaos of the genre. You play as adorable food items armed with boomerangs, fighting in top-down arenas. If you are looking for top-tier arena combat