Grant Kirkhope, the composer for the game, did not know the full title of the Rabbids game, and didn't know that Mario was included. Grant Kirkhope also composed the music for some of the critically acclaimed Rare games, like Banjo-Kazooie and Conker's Bad Fur Day.
The first home-console Mario RPG since Super Paper Mario (2007).
The title was rumored and eventually leaked to the general public, 6 months before the official announcement at E3 2017.
This game, along with its sequel Mario + Rabbids: Sparks of Hope (2022), are one of the only Mario games that was not developed or published by Nintendo.