Clowns are creepy. Dolls are creepy. A clown doll that moves whenever you aren’t looking at it is going to be creepy. This one is a minute long and doesn’t waste time with dialogue or background. The post-credit scene is either creepy or silly, depending on your feelings about clowns.
You can check it out on Youtube. And if you want to support the people who make these films, consider picking up the DVD collection, Nightmare House.