The Egg

The stone he put in its place looked exactly like Jon's stone, except that it didn't have the same luster. In fact it wasn't a stone at all it was an Egg. It worked just like the normal stone, except that it fed off wishes, and how the person wished would affect what was born and it's personality. After a dozen or so wishes it would hatch, and still be able to grant wishes but with a spin depending on how its born. The stranger then left wiping a tear away as they fled.