Once when watching a movie in my friend's basement, I saw movement in my peripherals, and looked over to the couch he was on. At first I didn't notice it, my only source of light being the television, and my main thought being it was strange that my friend hadn't seemed to have moved.
Then I saw it.
Behind the couch was a shadowy silhouette of a figure, darker than the backdrop of the lightless room. But its face.. my god. It appeared to be a mask, colored like skin, but shiny like porcelain. It was almost flawless, and practically featureless. A slit for a mouth, slightly agape, with no lips at all. The nose was pulled back, nostrils flared, and seemed as though it were a snakes. And the eyes, while not menacing, were dark gaping pits of horror.
I stared into the figures soulless eyes, for longer than I would have liked, but I was frozen with fear. After what felt like an eternity, my friend took notice of my terrified gaze in his direction, and spoke to me. I did not hear his words, as they were muffled by my adrenaline. But as he spoke, the creature began to quickly drift away, around the corner to the next room. It never broke its gaze with me.
My friend came over to me and shook me, asking if I was alright, and my instincts finally kicked in. I ran to the light switch, flipped it on and grabbed the nearest weapon, a pull up bar laying on the floor. I babbled incoherently as my friend followed me, searching frantically from room to room. As I caught my breath, I began to explain in detail what I had seen, and my friend stopped dead in tracks.
"Are you being funny?"
"Not even a little."
"Dude really its not cool."
"I'm not joking dude, I am freaking out."
"Dude... I've been having nightmares of a thing like that since I was a kid."
We searched the whole house, never found anyone, and the doors upstairs were securely locked. I don't go over there any more.
TL;DR: I stared down a nightmare creature that was lurking in my friend's basement. May literally be the creature from said friend's nightmares.