It was the Stone of Servitude. It looked and functioned exactly like the stone Jon's grandfather had sent him, but it also possessed additional powers.
When someone wishes on the stone, every previous stone user will immediately become their slave. Each slave will find themselves completely unable to disagree, disobey or hurt their master in any way, or allow them to come to harm.
They cannot bring themselves to ask for wishes the master makes to be reversed and will embrace all the master's wishes fully, whatever their private feelings on the matter are.
A slave may only disagree with the master's wishes only if he asks their opinion of them and before the wish is made "“ and only if the wish would be disadvantageous for their master. In fact if consulted, a slave will always try to improve the master's wish - but will not dare to speak up without being asked first.
Though slaves are not compelled to act or behave in any way benefitting their master while not under his observation, unless previously ordered. And should a slave get their hands on the Stone of Servitude and make a wish, they would become master and their master their slave...
