Excellent writing! I won't even say how vivid Spike is with his smokes and shadows, and I just loved the way you describe his un-humanness versus Buffy's normalcy. Also like very much her general attitude: it feels real, and she's facing her fate and assessing her chances just like she does in a fight. Looking forward to reading what happens next!
(And, add me to the list of people struck by the Spike gargoyle, of course.)