A level 19 CMD Grand Horn will drop Vagyrisk Claws, not morph into them. I'm fairly certain that you can't fight level 19 CMD Grand Horn after the Temple of the Ancients, anyway. Also, you can get them by stealing from Bagrisks if you have a low Dexterity. And for anyone wondering, the Premium Heart is powered up by how full Tifa's limit gauge is and how high her limit level is set.