If, in some hypothetical universe, Mario was a newcomer in a non-Nintendo-made Smash, they could do the music-changing thing Mementos does but for all the Mario subseries. You could have an NSMB theme for 2D platformers, SM64 theme for 3D platformers, then Mario Kart; Yoshi's Island; Wario Land; WarioWare; and DKC themes for those respective franchises - maybe even a classic DK theme for pre-SMB Mario games and a Dr. Mario theme for quirky (non-RPG) spin-offs.