Mistress Nyx was concerned about the disruptive tendencies this guy had. She tried to talk to him and she told him that she did not want any of that. But he did not listen and he instead chose to piss her off. She was not going to let him do it again so she fisted him. He could not believe what she did to him but he had learned his lesson in a painful way.
When this guy conned mistress Nyx, he did not expect that there would be consequences for what he did. He thought the issue would die a natural death as soon as possible. And that is why she chose to fist on him and teach him a lesson about honesty. He was in pain and the pain did all the work for her. He never wanted to feel that way again and so she stopped being a con.