what if happy mask salesman is a ghost? i mean, it would explain how he vanishes into thin air at the end of the game. and the fact that he can change his facial expression and body position in a split second, and the way he has a grand piano in his pocket. and the fact that that he is aware of the time loop, and he knew that link is the hero of time. and that he followed link without link or majora knowing.
NOW IS A TIME FOR CELEBRATION! http://www.youtube.com/watch?v=HFKtYCcMWT4