Here, we just have to post a sentence, and sentences turns into stories. However, make an ridiculous to the last poster's sentence. Occasional posts with no ridiculous stuff are OK.
Example:
Random person 1: There once was a boy who liked ice cream.
Random person 2: He never ate one, but he liked it.
Random person 3: One day he walked aimlessly in the Hogwarts grounds.
Random person 4: Then he saw an ice cream floating in the air.
Random person 5: It smacked him in the face.
And so on.
Me first.
Once there was a girl in Slytherin.

Once there was a girl in Slytherin.

She had a bad memory and usually smelled of vinegar from trying to enter the wrong common room.

She tried to look for a house elf to befriend

She went down the kitchens, however, met a vampire instead.

She gave him a nice hug

But he smelled like dirty socks and rotting apples.

So she ran away to her common room.

And cried

However, she found herself in the Gryffindor common room.

The Gryffindors were surprised that a Slytherin entered their room and began to pick on her.