The music for each stage is the theme of whichever character lives there. In Mario's stage, you will hear the classic Mario Bros. theme that any Nintendo fan can hum. It doesn't end there, however. The sound effects are just as good. Everything is spot-on.
Lasers sound like lasers, bombs sound like bombs, and swords sound like swords.
Not only that, but most characters have voices as well. The only thing that tops the quality of the voices is the music. Like I mentioned before, hearing a character's voice get quieter as they fade into the background is hysterical. Definitely a top-notch production. This is easily one of the best sounding Nintendo games ever.