This key will unlock the Deluxe Edition, which alongside the base game includes all DLCs.

Steam blurb:

A Rhythm Role-Playing Game! Fight party crashing monsters with the power of music! Level your party and upgrade your gear while dancing to the beat of some groovin' tunes. Grab a friend and combine forces in all game modes in The Metronomicon: Slay the Dance Floor!

Good luck!