The Mindswap Stone

The stone he put in its place looked exactly like Jon's stone, except that it wasn't. It was the Mindswap Stone. It worked just like the normal stone, except that when someone makes a wish with it, the mind of the wisher gets swapped with the mind of someone else, within 100 feet of the stone. Both minds will know that the swap happened, although they probably won't know why or how. And both minds will notice changes in reality, whether they heard the wish made or not.