Everyone is here! Super Smash Bros. Ultimate is the 5th game in the Super Smash Bros. series, released in December 2018 and developed by Bandai Namco. In the fourth game, Super Smash Bros. for Wii U and 3DS, a new trio of playable fighters was introduced: Mii Brawler, Mii Swordfighter, and Mii Gunner. While all promotional material of these three Mii characters used the same Miis, their Mii data was not in the game files. This changes in Super Smash Bros. Ultimate, however, with a different trio of Miis. There was even an unused copy of the Mii for Mii Swordfighter, named Sordsman. While that's where the Miis stopped at the game's launch, future updates which added DLC fighters and Spirit Boards sometimes also added Miis. Updates v10.1.0 and v12.0.0 both added new Miis based on Final Fantasy VII and Tekken characters, to coincide with the inclusion of DLC characters Sephiroth and Kazuya and their respective Spirit Boards. These Miis are used as opponents on these DLC Spirit Boards.
Also, while Super Smash Bros. for Wii U and 3DS never had actual Mii data, it did have some 3D models resembling Miis from Wii Sports Resort on certain stages, which return in Super Smash Bros. Ultimate. Those additional 3D model Miis are shown below.