From the looks of this piece by Christina Dee, it seem that Peach and Toad are sick and tired of Bowser showing up and kidnapping/kicking their respective asses. And they’re going to do something about it.
Peach is full commando mode with a WWII era machine gun, I think, and Toad is going for more of a Prince of Persia approach. Where’s Mario? Probably learning a lesson that he probably should have brought a hand grenade to Bowser’s castle instead of some Koopa shells.