Nintendo's famous gaming character from the Mario universe has surprisingly been spotted in an unreleased, exclusive racing game for the Sega Dreamcast console, which is why the implementation of Luigi was apparently an easter egg or inside joke among the developers.
https://www.notebookcheck.net/Nintendo-s-Luigi-has-been-discovered-in-an-unreleased-retro-racing-game-for-the-Sega-Dreamcast.563115.0.html