So I just picked up the Omens of the Pharaoh expansion, and as I was looking through it I realized most of the mask monsters were really old Chaosium-era pulls. Which is fine, but is a little on the dated side. Since I've never seen these all listed anywhere else, I thought I'd post a few more modern avatars that have been cooked up since the old days, just in case FFG wanted a little more gas for a future expansion. Also, potential spoilers for some pretty good videogames, so read at your own risk. If anyone else knows of some oft-overlooked Masks, post them here as well!

(Specifically Darkest Dungeon, Witcher 3, and Persona 2)

The Walkin' Dude, Randall Flag (Stephen King's "The Stand" and others)

Gaunter O' Dimm , Master of Mirrors / The Man of Glass (Witcher 3, Heart of Stone DLC)

Great Father (Persona 2: Innocent Sin)

Heart of Darkness (Darkest Dungeon)

On 9/19/2018 at 10:00 PM, Sinthioth said:

Gaunter O' Dimm , Master of Mirrors / The Man of Glass (Witcher 3, Heart of Stone DLC)

As far as I know this one is inspired by Randall Flagg and some other characters and myths.
You could decide that he's a Nyarlathotep mask in your own content, but saying that he's a mask in the Witcher is quite a stretch.

On 9/19/2018 at 10:00 PM, Sinthioth said:

Heart of Darkness (Darkest Dungeon)

I would call that an even bigger stretch. Why do you think it's Nyarlathotep and not another, existing or new, entity?
I'm not saying it certainly isn't. I'm saying I haven't seen any evidence that would support such notion.