I finished this up awhile ago as a birthday gift for my brother/ awesome prop mask for myself. I have basically the same write up for it on my blog: boundclockprops.com. Just thought I would share it in this forum as well.
This is the mask of the evil villain Amon from the show legend of Korra.
Step 1: The Beginning
To begin with I mixed up and rolled out some Apoxie Sculpt and placed it onto the foam head with a layer of saran wrap, between the putty and the head, to keep it from sticking so I could save the head for future projects. After the initial rubbing and shaping of the Apoxie I let it cure so the really work could begin. To smooth the surface and do more shaping I applied multiple layers of bondo. After which a sequence of sanding, then bondo, then sanding some more, the bondo, then sanding, sanding, sanding, and just for good measure sanding some more.
Once the final shape came through I began making/refining the details for the mask, which for this mask was basically 5 or different parts, including the eyes, nose, mouth, the circle on top, the crown like piece around the circle, and the cheek pieces.