Note! This game is a TKThunder project! Please don't edit without my permission! Gratzi!
Mario and Luigi: When Rivals Collide is an upcoming game for the Nintendo 3DS. It is very similar to Bowsers Inside Story in gameplay. It will be released sometime in 2017.
All Mario and Luigi games have a certain theme: this one focuses around teams. The new gameplay involves Mario and Luigi battling with Bowser to defeat Midbus and save the Mushroom Kingdom from being frozen over.
One day in the Mushroom Kingdom, Princess Peach was holding a party in her castle. She invited many Toads to it, as well as Starlow, Toadbert, Toadsworth, Broque Monsieur, and, of course, Mario and Luigi.
The party seems like it is just getting started when Bowser crashes in. Mario (Luigi is knocked out) is given an optional tutorial on how to battle by Broque Monsieur, and Mario defeats him. Peach is about to eject him from the castle when suddenly everyone feels very cold. Starlow looks outside to find that the surrounding area is completely icy. Suddenly, Midbus and some Mibbas crash in, taking Peach and destroying the castle.
Mario, Luigi, and Starlow wake up in Herbia Forests, and walk around a bit. They find Bowser stuck inside a tree trunk and pull him out. Before Bowser can pound him, and old Treevil named Trelder finds them and explains to him what is going on: Midbus has decided to freeze over Mushroom Kingdom and make Peach his maiden. So Mario, Luigi, and Bowser reluctantly go on an adventure to find the Rainbow Beacons to melt Mushroom Kingdom.