I was poking back through the MT.Net archives to find this really cool Halloween effect I did six years ago. I called it the Floating Ghost Effect.
Here’s a picture of it in action as well as one that shows how it was set up.
Update 5 Feb 2012: Hello, Facebook users! I’m not sure how my link got so popular on FB, but if someone would kindly email me and share, I’d much appreciate it. Thanks for visiting!