The petrification ability it's not controlled by the opponent that controls Xanthrid Gorgon but by the creature itself...
Please autocard: [c]Shard Phoenix[/c] = Shard Phoenix.
The Basic rulebook, read it! A lot of basic questions are answered there!
How to autocard :
Type [c]Black Lotus[/c] to get Black Lotus.
Type [c=Black Lotus]The Overpowered One[/c] to get The Overpowered One.