Pinkie's Parasprite Polka, AKA Pinkamena's Party Polka, from My Little Pony: Friendship is Magic. I did this in kind of a rush because I wanted to get it done before someone else like RainbowCrash88 (who is awesome by the way) did it first.  To make this, I used Famitracker, an excellent tool for making authentic NES music.