I once went to a horror party that was really cool. The girl who hosted the party was really into horror movies and sort of into the Gothic style (not over board or anything). All of the guests dressed in black, the girls had black eyeliner and nail polish on. She made a really cool haunted house in her garage With horror movie theme music.
Her mom actually dressed up as the "It" clown and pretty much scared everybody in the haunted house. They dressed her little brother up as "Jigsaw" from the Saw series. He was really freaky looking. They actually had him on a tiny tricycle riding around through the haunted house. The Jigsaw costume was really impressive because it's pretty much impossible to find but they had purchased it off Amazon.
We had a mosh pit dance that was pretty big outside, a few people actually dressed up as vampires and a couple of other cool costumes.
A few of the girls spent the night and we watched a couple of horror movies which kept us up all night!