To start with, I downloaded a 3D printable human head model(.obj). In maya, I reduced the number of polygons and made it live to retopologize manually. Then I was able to send it to mudbox to deform and add the details.

Here is my reference mask:

To complete the whole mask, I needed to create the assets such as horns, eyes and teeth. I just created simple topologies in maya and would send to mudbox for further editing as well.