Though no sequel has been announced as of the writing of this article, The Super Mario Bros. Movie did so well at the box office that a second movie is almost a guarantee at this point. Both Nintendo and Illumination would stand to make a lot of money from a sequel if the success of the first film is any indication, and so it seems likely that they would take advantage of that opportunity. The world of Mario is so expansive after so many years of the franchise existing that it wouldn't be hard to pull inspiration from one of the many games for a brand-new story.
A sequel would also be an opportunity to showcase some of the characters or plot points from the Mario universe that didn't make it into the first movie. There have been so many Mario characters that have appeared over the years, they obviously all couldn't make it into one movie, but future entries in a franchise would be able to show them off. There were also some plot details that were brought up in the first movie but weren't expanded upon, and a sequel would be the perfect place to explore those questions even further. Here are some ideas about what a potential sequel to The Super Mario Bros. Movie could tackle.
A New Villain
While the first movie had Mario and the gang facing off against Bowser, a sequel could give them a chance to oppose another villain from the franchise, especially if Bowser is still incapacitated after the events of the first film. In fact, they could still keep it in the family by making Bowser Jr. the next villain. Debuting in Super Mario Sunshine, Bowser Jr. is a staple of the Mario franchise and appears in a ton of the games, from mainline Mario to Mario Kart. He would be a perfect addition to a new movie, and he already has the perfect motivation - avenging his dad.
This would also open up the chance for the Koopalings to make an appearance as well. The Koopalings are essentially minibosses throughout the platformer Mario games, who now make appearances in other Mario games like Mario Kart. They all have distinct designs and personalities, and they would make for fun antagonists on screen as well. They could be the adversaries Mario has to get through to finally get to Bowser Jr., or they could just be the main antagonists too if Illumination would rather play it that way instead. Either way, they certainly have a whole host of potentially villainous characters to choose from for the next movie.
Adding Fan-Favorite Characters
While there were a lot of classic Mario characters that made appearances in the first movie - such as Toad or Donkey Kong - there were a few other mainstays that haven't yet been introduced. There is a brief scene that includes glimpses of Yoshis, and the post-credits scene of the film gives a hint towards a future Yoshi appearance with the image of a Yoshi egg hidden in the sewers of New York, presumably having come through the pipes from the Mushroom Kingdom. Yoshi is such a huge omission from the film that it would be a huge mistake not to include him in any future entries. Mario's adorable dinosaur companion deserves his screen time too.
Another missing fan favorite is Peach's princess counterpart Daisy. Daisy is another character that would be really easy to add to a sequel, and could be introduced as a new friend for Peach or a love interest for Luigi - or both at once - depending on which direction they choose to go in. Better yet, she could just be her own character who happens to be a ruler over a neighboring kingdom. If there's one thing the Mario franchise could use, it's a few more female characters, and adding Daisy would give them the perfect opportunity to do just that.
More Of Peach's Backstory
The Super Mario Bros. Movie includes a short scene where Peach discusses her origins - mainly that she doesn't know exactly what they are. She doesn't know where she comes from, and a sequel would provide the perfect opportunity to explore that plot thread even further. It could even be more of a Peach-focused movie where the gang has to help her find out where she came from. It seems that she likely came from another world, as it's hinted that there are a myriad of different worlds other than just the ones seen in the movie. This could even be a hint towards her coming from another planet, or perhaps another galaxy.
This could be the perfect opportunity to bring in lore and plot lines from the Super Mario Galaxy games. The Super Mario Bros. Movie even included an appearance from a Luma, which are star-shaped beings that are introduced in Super Mario Galaxy. Perhaps the next Mario movie could see Mario and his crew exploring other planets, and maybe even meeting up with other fan-favorite character Rosalina. With so much Mario content to pick from, there are basically endless possibilities when it comes to the question of where the Mario movies could go next.