Rosalina & Luma are a startable playable team that they can fight individually, but with the same movements, in Ultra Smash Bros. IV. They were confirmed five days later after Captain Toad and Nabbit and after the reveal of Peach and Bowser. Generaly, Rosalina is the keeper of the Comet Observatory, and the mother of all the Lumas, far away in the galaxy who aided Mario during his adventures in Super Mario Galaxy.
Her voiceclip hasn't changed. It stays the same as in SSB4, voiced by Kerri Kane who also made voices for Bowser Jr.
Rosalina & Luma are in the 20th place of the 103rd (B+) in the tier list, behind R.O.B. and after Mii Brawler putting them at the top of the high tier classment, which it makes them a slightly drop comparing to SSB4 but maintains their spot as top tier team in this game.