Super Mario 3D World + Bowser's Fury allows players to choose between a roster of four characters, at least at the beginning of the game. There's Mario, Luigi, Toad, and Princess Peach (sorry Daisy). However, there is a fifth playable character that players can unlock once they wrap up the main story mode and that character is Rosalina, who first made an appearance in Super Mario Galaxy for the Wii.
There's no way to unlock Rosalina at the beginning of Super Mario 3D World + Bowser's Fury, as the only way to get her is to first complete the main game and then playing through the Star World. The Star World is the first of four worlds that players can unlock in the post-game. It's full of challenging levels for the most hardcore Mario player. To actually get Rosalina, players will need to complete Star World 2.
There's not much to unlocking her besides completing that world, but once players finish that, then they'll have access to Mushroom World, Flower World, and then Crown World. The latter is difficult to unlock in Super Mario 3D World + Bowser's Fury because players will need to first obtain all stamps, Green Stars, and make all Checkpoint Flags gold from World 1 to World Flower.
For those wondering what Rosalina can do, she's actually one of the best characters in the game thanks to her ability to double jump and attack enemies without the need for a powerup. Because she's such a strong character, players should choose Rosalina if they're a Mario novice or just new to platformers in general. She's easy to handle and can protect herself through various methods.
Any Rosalina fan should make sure to check out these fan reactions to early Rosalina concept illustrations from a Super Mario Odyssey art book.
It's worth noting that Rosalina, or any of the other characters for that matter, are not playable in the new Bowser's Fury expansion of Super Mario 3D World. The game mode is completely separate from the main multiplayer mode and puts players in the shoes of Mario as he collects Cat Shines while also facing off against Bowser once again. However, this mode does support two-player co-op play, as a second player can join in on the fun and control Bowser Jr. and aid Mario.
Super Mario 3D World + Bowser's Fury is now available as a Nintendo Switch exclusive.