If you haven't already seen it, it's called Super Mario Odyssey - A Galaxy Story and is a "mod by Slycer and many more". It brings the universe of Super Mario Galaxy to Mario's 2017 Switch release ...

Rosalina is a character that debuted in Super Mario Galaxy. Rosalina first appears in the Gateway Galaxy, and she is also the adopted mother of the Lumas. Rosalina commands the Comet Observatory.