An alleged leak indicates that Mario's first RPG adventure on the Nintendo Switch will be a collaboration with Ubisoft titled, Mario + Rabbids: Kingdom Battle. The leak includes images that were supposed to be presented in June at E3. 

According to the images, this upcoming title will be a crazy combat adventure, turn-based RPG full of humor and self-mockery. Kingdom Battle is supposed to have a 20 hour story mode, local two player co-op, and eight playable characters with non-traditional weapons, unique abilities and personalities. We can surmise that those characters will be Mario, Peach, Luigi, Yoshi, and their Rabbid parody counterparts. 

Here are the images from the reported leak:

In regard to gameplay, the game is supposed to be a balance of 35% exploration and 65% combat. On the exploration side there will be four world environments to discover that will include puzzles and secret zones in a twisted Rabbids world full of Nintendo easter eggs. On the combat side there will be different play styles depending on the character you choose, tactical options, upgradable weapons, and seven enemy archetypes in addition to one boss/mid-boss per world. All of this will unfold through a variety of combat objectives and contextual events. 

Mario + Rabbids: Kingdom Battle is supposed to debut in a hands-on experience at E3 in June, will be promoted with previews throughout July, and will finally release in August.

Source: comicbook