The Buffy the Vampire Slayer Sing-A-Long is coming to Boston this Saturday night, with extra prom attached. Starting at midnight, there will be a showing of "Once More With Feeling," complete with singing, dancing in the aisles, tossing of various approrpiate (or not) items, bubbles, kazoos, and that warm glow you get when you're in a room filled with people who love the same esoteric thing you do. Afterwards, there will be a dance party, accompanied by hits from the 80's and 90's, trivia, treats and games, plus the crowning of a King and Queen. The admission is $12, the memories are sure to be priceless.