I have a mask on the wall in my room. It's small like a child's face, but has the proportions of a grown woman. The 'skin' is completely white, it has perfectly shaped black holes for its slanted eyes, it has purple and gold eye and lip makeup, and a little black spot for a beauty mark. It's been up there since I moved into this house (I was seven? Six? forgot.) and I don't ever remember it being creepy. Maybe Serge doens't think the masks are creepy cause he got used to sleeping beneath them. Stare at something long enough and the creepy aspect will go away. Take that something away, and the room just won't feel right anymore.
Are there masks in any other rooms in the game? Faust's guardian spirit hypothesis sounds possible.