Around Sunnydale, they say a scarecrow saturated with Halloween rain will come alive and slaughter anyone in sight. (Lovely place, Sunnydale.) Buffy's best friends, Xander and Willow, used to think the tale was nonsense - but after a few adventures with Buffy, they're not so sure. Even without a maniacal scarecrow, a Sunnydale Halloween is a truly horrific happening. There are enough zombies and vampires about, ready to party hearty and eat some brains, to…