Nintendo actually putted a sound that will sound familliar to some other Nintendo game. Peach's Final Smash actually had a soundtrack from Super Mario Bros 3 Secret Stage(if I'm not mistaken). So, I want you to perform this. The best thing you should do is go to training in Solo. Play as Peach and go to the item select. Select the Smash ball and equip it. Now, turn the speed into the slowest possible speed there is and compare SMB3 Secret Stage and Peach's Final Smash. It's kind of nice that Nintendo did put that there.
Unfortunatly, none of the credits go to me. I just find it interesting so I wanted to spread the easter egg.