I thought it was Setites, with snakes using reverse Serpentis. (Although I admit it's been a really long time since I read it.)I think Berlin by Night had a vampire nazi making vampire snakes who could use reverse-protean to turn into snake men?
That's also hardly a standout moment. The rest of the thing isn't quite as much like a Saturday morning cartoon as the vampire cobras, but it isn't all that much better, either. And my recollection is that the ending is that the PCs more or less stand around and get shown that the main visible antagonist got defeated by someone else. Which is always awesome.