I just got back form Kumoricon and wanted to post what I did to the creeper cospalyer. I couldn't resist and I doubt few others could have too, since it was a full body one, I'll upload pics later. It was a simple gag but still always fun. I just came up form behind, pushed on the side of the costume and as the person turned I moved to stay out of sight. The cosplayer could only see in front, and had someone else giving directions. It was great fun and I'll add a link here once I upload all my photo's.