Thank you Kotowari! I'll try the inverted song, though I want to try without a walkthrough first. ;3
I also believed that the Majora's Magic and the Twili's Magic were just opposites of each other. The Twili left behind the Twilight Mirror, and the Majoras left behind the mask. Though of course I haven't actually beaten the game so I don't know anything other than the basics about the mask.