The stone he put in its place looked almost exactly like Jon's stone, except that it wasn't. It was The Lucky Stone.
It worked just like the normal stone, except that any wish that's a "mean wish" (one that would cause harm, in one way or another) would cause the wisher to have bad luck for one hour. Any wish that's a "beneficial wish" (or one that would give help to someone or something, in one way or another) would cause the wisher to have good luck for one hour.
The good luck and bad luck "hours" are accumulative. So, if Jon made a "mean wish", a "beneficial wish", and then two more "mean wishes", then he'd have one hour of bad luck, followed by an hour of good luck, then two more hours of bad luck, all in a row.
