The clues: Though Miss Monster doesn't give us too much to work with in their video montage, we do see them applying "Furspray" and a glimpse of their key ring that says "FUN." It's also worth noting that the locker Miss Monster opens is numbered 10.
Who it might be: Though the judges throw out music legends Dionne Warwick and Tina Turner as potential people behind the mask, others are theorizing that it might be singer Chaka Khan. Not only does the height match up — Khan is 5'4" — but the 10 on the locker could be a reference to Khan's 10 Grammys.