The "change face mask artist" is actually a magician who flips up different masks from his hat, costume, belt or shoe, with a blink, a nod or a handshake.
This form of opera is only known to only a handful of practising masters in Sichuan province today.
I managed to take a few photographs from among the 20 or more different masks by a performer specially invited for the occasion. From the side profile, I saw one of the "slower" transitions but not enough to find out the tricks employed. Surely, he would need a lot of practice before he's able to put up such an impressive show.
The following video probably gives a better idea of the speed of change from a famous artiste.
变脸, 變臉, Biàn Liǎn more commonly known as face changing is a 300 year old tradition ...