Sans

Sans (also known as Sans the Skeleton) is a main character in the indie hit, Undertale, he takes on the role of a laid-back lazy pun-loving character who doesn't fight due to a promise with Toriel, but in the Genocide route of the game, he's the real final boss. He is also a Mii costume in Super Smash Bros. Ultimate.

Super Smash Bros. Ultimate
On September 5, 2019, a video was posted by Nintendo entitled "Super Smash Bros. Ultimate - Mii Fighter Costumes #3 - Nintendo Switch" which at the end announced that Sans would be a Mii Fighter costume along with adding one of his leitmotifs, Megalovania, to the game as a song.