You knew it was bound to happen in the age of the YouTube video mashup: just because Buffy the Vampire Slayer and Edward, the broody vamp from “Twilight,” exist in different media doesn’t mean they shouldn’t work together. I mean, they both went to high school, and they are both involved in the classic battling of desire vs. duty. And it just so happened that it’s the day after the birthday of Buffy creator Joss Whedon (also of “Dollhouse,” “Firefly,” “Angel,” and the breakaway superhit “Dr. Horrible’s Singalong Blog”)–but whether the timing of this video’s release was intentional or not, the blending of these two universes represents an homage to Whedon. Somewhere, someone saw Edward and said, “This guy has got to meet Buffy.”