This is a really interesting monster and one of the best I've seen so far. I like the idea of a kind of anthropomorphic personification of a problem in urban areas, both real and imagined. It's a little darker and grittier than you might expect and a brave choice indeed. For me, it's a stand out for its concept alone.
I'm running Curse of the Crimson Throne at the moment and this would fit in really well, so I'm definitely going to give it a go. It's threatening but not over-powered; the chances of an entire party failing a DC12 save and then failing on the D% are fairly low and if the worst happens, well it just adds a legitimate level of threat to the game!
Gets my vote!