Fox Face will use SP Lowering to prevent you from using a fusion. But you should have enough SP to allow you to fuse with a monster. Have Yuri fuse with any fusion monster that you had selected before the incidents at Kuihai Tower. Heaven's Fiend if you had him in your slot. Keep pounding him with special skills for this is the quickest way to defeat him which you want since he will still use the dreaded !!! attack. In 4 or 5 attacks he will go down, do not forget to heal when necessary because he has high attack and that !!! can be deadly.