It always depends on how heavy-handed you want the moment to be. If it's a more subtle gesture (less slasher thriller, more psychological), try performing a similar effect that Iain suggests with the other backgrounds in the scene. For instance, if the cemetery has crickets or a roomtone of its own, try distorting/pitch shifting those sounds as the creature goes by. Using the normal diagetic sounds gives the sense that the presence of the creature messes with reality.

Good luck!
~Matt

If it's an ethereal creature without a solid physical body then I probably would start with micking up some different fans and ventilation-systems (as worn and gritty as humanly possible), as well as vocalize lots of very whispery/breathy noises and half-words!

A creature made of shadow? "Ah-WOOOOOOOOOO! Shaka chaka chaka chaka."

Maybe not.

I can't remember the sound exactly per se, but there was an episode of the X-Files about deadly shadows called "Soft Light", I remember it had a lot of creepy atmospheric sound typical to the series. Another technique that seems to work well for tension of this sort is a sort of high-pitched metal groan with reverb, you can hear it around 0:24-0:25 in this clip:

http://www.youtube.com/watch?v=pqqEriE0ogc

Good luck!

I worked on a feature called shadow people and I ended up using the moogerfrooger app DI into my protools session and messed with the output gain to create crazy feedbacks. Worked really well.