This happened about 2 years ago, but i still get freaked out from it today:

I was having a party, and i had 3 friends over (i was only 11 at this time, so it wasnt like all the partys now). we were all sitting around gossiping about the hottest starts, etc, like girls do when they first reach puberty, when we heard a knock on the door. my mum went downstairs to answer it, and while she was gone this figure appeared. i do not know what the sex of this thing was, or what it was, but it was there.all of a sudden my friend olivia turned blue and couldnt breathe properly. this lasted until my mothers footsteps started coming up the stairs, then she went white, before returning to her normal colour. This was a very scary experience and i hope nothing like this ever happens again!