This is the polygonal skull mask design created by Etsy seller Wintercroft that can be cut and folded out of cardboard or heavy card stock. You can purchase the instantly-downloadable PDF template HERE for $7. Oooooor convince yourself that's entirely too much to pay, and try to find a pirated torrent of the design online. I couldn't, but I do have like twenty p0rnos downloading now.
Keep going for several more shots plus the BONUS animal masks available from the same shop.
Thanks to Catherine, who made a Grim Fandango reference in her tip and earned herself a gold star sticker.