The stone he put in its place looked exactly like Jon's stone, yet it looked smooth and flawless. It was "The Boundless Stone", which had none of the restrictions that Jon's stone had. The wishing range was as large as the universe, all wishes could be reversed with another wish, and everyone would notice how things were different after a wish was made, whether they heard it or not.
It would seem that something like this would be more powerful than Jon's stone, and it was. But Jon's stone had restrictions for a reason. If he ever made an accidental wish to destroy the world or even the universe, his stone wouldn't grant it, because of the limited range. But with The Boundless Stone, it would grant it. Of course, he could just reverse the wish, but what if he died or was seriously incapacitated as a result of his careless wish?
As the shadowy intruder backed out of Jon's room, he smiled to himself. He couldn't wait to see the mass chaos and havoc this new stone would cause.