Just as Cerberus is the elector of the new Clow Card Master, Yue is the judge who tests the candidate if they are worthy of the position. Unlike Cerberus, however, Yue is heavily dependent on the power of his master. During his first few appearances in this form, Sakura’s powers were not enough to sustain him, and his human self, Yukito, had to compensate by means of food and sleep.
A cosplay judge is not supposed to play favorites, but oh my goodness. I had a sneaking suspicion this cosplayer had something up his sleeve when I saw a pair of folded wings behind him. Imagine my surprise when those wings opened and closed on stage! Kudos to you sir!
I want wings like that too!
Source: 黑火子 ~Kurohiko
EDIT: Cosplayer found! Please say hello to Oliver Catalan!