This happened to me about 9 years ago, and I have posted this on a couple other websites. (Was waiting for this thread to come up.)
Me and my family had moved into my grandmother's house. Now this house was very old, probably the oldest on the block. It was also very small, even after my uncle built (poorly) 3 bedrooms and a restroom addition to it. The floors were pretty much hollow, so hollow you can tell if someone is walking around from any part of the house.
Now at night my grandmother had to have her restroom light on because of diabetes leaving her blind in one eye. This left the hallway lit with a sea foam green color because of the paint job of her bathroom across the hall.
One night I was awoken to the sounds of someone literally marching in the hall. It was so loud, and I had thought it was my grandmother walking around. I had my door open because I was afraid of the dark :( I stand up rub my eyes and say "Grandma it's three a.m and I have school tomorrow, go to bed!".
No Response. I stood up and waited for her to walk in front of my room, and I was ready to tell her off. As the loud marching got nearer I realized it was not her. In fact I heard her in her room next door saying "Oh god!"
That when "it" step in front of my door. I was a large black mass. It was like walking smoke, and almost human-like with freakish height. I could tell it probably did not notice me because it's "head" was pointed forward. At this point I could see through it. It was like looking through a black veil, but would shift around like smoke.
I was in awe for the couple seconds it marched slowly in front of my door. It left my view and continued moving toward my grandmother's room. As it passed her door she swore and screamed pretty loudly. At this point I some how got the balls to see it disappear into the darkness of the kitchen, and ran into her room (parents locked their door. Wonder why?)
She had told me she had seen it before and lit a candle to deter it from appearing, but the candle had burned out. Taught me a prayer, and we never spoke of it again.
TLDR: Shadow Person seen in hallway. Never sleep with door open again.