From the publisher:
Be afraid. Be very afraid.
They lurk in the shadows behind the tavern. Down the dark alley between abandoned buildings. Behind the trees in an otherwise mundane forest. Their goals are often alien, if they have any real goal at all. Some say nothing, allowing the viciousness of their attacks to speak for them. Others are alarmingly charming, right up to the moment they plunge a dagger in your back. They are the stuff of nightmares, as well as hundreds of horror movies.
The Horror Stalker class allows a game master to unleash unholy hell on his heroes. These relentless, tireless monsters will pursue their chosen victims without remorse and without mercy.
This 4-page PDF includes the Horror Stalker class as well as three sample Horror Stalkers (CR 5, 11, and 19)