The Original piece was from the Background music of when the key was realized, by William Anderson. I had made a cover of the song in Rarity's Key, and I decided since we're close to the end, that I'd make a full version of the piece.
Download: https://soundcloud.com/jake-sloan-3/rainbow-power-key-battle
also, check out my website : http://jakeneutronanimations.weebly.com/