After having his money stolen by Kamek, Wario and his brother Waluigi set out to get it back, only to be kidnapped by Bowser aswell! Wario is the slowest character in the game, but also has the strongest ground-pounds and can shoulder barge enemies.
Mario and Luigi's female cousin has also been kidnapped, after saving her from Boom Boom she becomes playable. Maria can glide in the air for a short while using her dress and has star spins almost as powerful as Mario's.
The Princess of the Mushroom Kingdom has once again been kidnapped by Bowser! Peach was out for a walk with Toadsworth when the evil Koopa king abducted her and took her to his castle, now its up to Mario & friends to rescue her.
Toad appears on various levels, assisting Mario & friends by providing them with useful items such as 1-Up Mushrooms if you speak to him. Toad is also seen at the start of the game, informing Mario of Princess Peach's kidnapping.
Yoshi appears in some levels after breaking open a Yoshi Egg. Mario and co. can then ride on Yoshi's back, he is able to flutter jump better than Waluigi and eat enemies and turn them into eggs/spit them out. Unlike in most games, only Green Yoshis appear in this game.
The Princess of the Lumas appears along with her Lumas on the Comet Observatory once the game is completed, it is revealed that she and Geno are good friends. Rosalina allowed Mario & friends access to Special World 10 in space once the player completes all of the Special Worlds that Geno gives access to.
The Star Being makes a startling unexpected reappearance! Geno appears at the Comet Observatory where it is revealed that he and Rosalina are old friends, he invites Mallow to the observatory once the player has completed the game. He also gives the player access to the Special Worlds.
The flailing-armed Koopa is battled on Bowser's airships, he also kidnapped Maria under Bowser's orders. Boom Boom will flail his arms around to try and hit the player during battle, he'll also retreat into his shell and roll around.
Fire Mario gives the player the ability to throw fireballs, the player can throw up to 5 fireballs at a time before having to wait for them to disappear to throw more. It is acheived by getting a Fire Flower.
Shell Mario gives the player a Koopa Shell on their back, the player is then able to duck inside the shell, shell-dash much like a kicked Koopa Shell and ground-pound inside the shell. It is acheived by getting a Blue Shell.
The game marks the first time that character Waluigi has appeared in a main-series Mario game.