This happened to me and my friends a few years ago, in the summer of '06 when I was about 15. This one day, we were walking past an old abandoned house that is about a block from my grandparents house. The owner of the house was sent to a mental hospital in Texas, and all of his things were still in the house. At the time before the incident, no one knew why he suddenly went insane. It is an old house, and the windows and garage door are covered in thick black wood. All except a window that is in the backyard, which is of course not mowed so the grass is really high.
The house is on a corner and on the right side, near the entrance to the backyard, there is an alleyway. You have to go through the alleyway to get to the fence that leads to the back yard. So my sister and my best friend and I decided to check out the backyard, which already looks scary because the grass is so high, it looks like a jungle. We discovered the open window when we were looking at the back of the house. Of course since I was the smallest, they lifted me up and made me look in the window. No one was around and it was about dinner time, so maybe 5 or 6 O'clock at night.
When I looked in, at first all I saw was the stuff outside, until I cupped my hands around my eyes to see in. The furniture was still there, although it was covered in years of dust. Then I saw it.
Staring at me, as if it knew I was coming. All black, except for its eyes which were pure white, with no pupils. It was about 6 feet tall and barely had the shape of a human. It didn't appear to be standing either, just floating about a half inch off the ground. I saw it begin to open its mouth, which just had a few sharp teeth in the front. I screamed my head off and my best friend (who's shoulders I was sitting on) dropped me and began to scream herself. My sister kept saying, "What, what, what was it." I refused to answer her until we ran home.
When I told my neighbor the next day she told me her short story. "I used to know the people who lived next to the house, they were really nice people too. They used to tell me that Mark (the owner of the house) use to claim that something was trying to take over his body, something evil." I remember, I put my hand up and stopped her from finishing, "I know exactly what he's talking about", I said. "When I looked at it, I felt like it was trying to suck out my soul, when it opened its mouth."
We still sometimes go back to look at the house, and after 3 years have gone by, I still sometimes think I see something in the window, but other times, I think I am going crazy myself.