A user played a blank card threatening to shoot up a certain school. Another player in the match reported it to the FBI, and, due to the legal costs racking up against the person running the servers, PYX has been closed.
It wasn’t the admin’s fault, it was a dumb player who has since been arrested.
For those who still want a CAH clone, there’s still azala.info, which still has chat and customs, as well as community-made custom packs and the ability to make your own “pocket decks” to shuffle into any game you join.
The loss of XYZZY is still terrible and there were many people that enjoyed it more, but there’s still at least an alternative.