Sonic Channel staff on their blog:
It is Shadow wearing a Halloween costume. ♪
The people who got it up to Shadow Chao are spot on!
There seemed to be many people thinking that Shadow disguising himself as a vampire with Shadow Chao’s wings from the middle hint image. There were also people answering “Shadow” correctly and successfully while hesitating over Mephiles.
About the decoration and setting, mostly everyone answered “basket with candies” and “Halloween costume” correctly.