You need to think of his vulnerabilities and weaknesses, about the things that elevate him and about those which bring him down. Of course, you need to use all of this against him and to your own advantage. Although this is one of the hardest things to do, you need to find a way to shut down all of the emotions you have for him and you need to let your reason be your only guide. If you really want to hurt him, there is no place for your conscience or guilt here. You need to be sure that this is exactly what you want to do and if it is, you need to shut down any remorse you might have regarding this revenge. Just remember that this man has hurt you many times and every sign of regret will instantly vanish.
Also, you need to make it clear to yourself that your narcissistic man will never love you and that he is only disguised as irresistible and that you need to take love out of this equation. Additionally, don’t ever expect him to change toward you or any other woman in his future. You won’t teach him a lesson by hurting him because he will do all the things he has done to you to every woman who crosses his path. But what you will accomplish is getting your own personal satisfaction and that is what your goal should be.