Sudden idea while watching an AMV of Blood the Last Vampire:
In the movie, viewed as a very short clip in the video, a man stands before a sign while being illuminated by a spotlight or car headlight. He holds his hand up to shield his eyes from the light. Directly behind him, the sign has a bloody handprint on it pretty much where his hand's shadow would be (at first glance, of course).
My idea: A creature whose shadow appears as a pool of blood, with sharper shadows producing sharper details (such as a spotlight producing a handprint complete with ridge detail on the sign). Obviously, all the normal avenues for cool, creepy shadow remain available here with just the added flavor of blood (an animated shadow, shadow-stepping, etc).