I completely agree with the former posts that say that you can't win. I have been fighting this battle since I was a kid (and didn't even know what the fight was about) and always lost.
If you are a believer, then don't get in the way of God's justice. Forgive and let Him carry out it.
But if you want to try something, I can say one thing you CAN’T do. NEVER, NEVER, NEVER tell the whole truth about the narcissist.
Nobody will believe you. That by itself is a defense for the narcissist. It is too much craziness. You wouldn't believe it if you weren't there.
I had a narcissistic/borderline girlfriend. She was my best friend during college. EVERYBODY who knew her (including myself) would tell you how religious, funny, considerate, honest, lovely etc she was. When we began our relationship I thought I had won the lottery. During the following months, between her attempts (?) of suicide, I would try to conciliate two images in my brain: the one of the angelic and beautiful classmate and the devil I had met. BTW, she always accused me of being aggressive (in the middle of her affairs, lies etc).
If I couldn't believe who she was behind the facade, who would?
I remember when I read “A child called it”. There was a moment when I threw the book away and said “Impossible! Nobody would do it!”. Immediately I understood why so many people weren't capable of connecting with my experiences and tried to minimize my feelings.
If you want to try to break the facade, the inverted picture of victim/aggressor, you may try a very simple step.
You say only a simple (but powerful) truth (a fact, never an opinion, judgment etc) a time. And you state that calmly, never making any accusation.
In the same way the N planted seeds of lies and doubts in the minds of everyone, you are going to try to plant a seed of truth.
If you have to stick to a single truth, do it. No matter how long it takes.
A friend of mine always joked that I must be the crazy one, not my girlfriends. If I were in her place I would have thought that as well. One day, I sat down and said, “Well, you say I'm the crazy one, let me tell just one, among hundreds of things that I hear, and this one is far from the worst. What would you think if your husband, after you helped him all day long to buy gifts and other things, when you arrived home, told you “I am just going to have a quick one with the neighbor, bye”, with a smile in his lips? And after that, if you complained, you had to hear that “you don’t have a sense of humor”? And if you still desperately complained, you were told to go away, because “it was impossible to talk to you like that”? What would you feel?”
That changed everything. But she wasn’t under the spell of the narcissist, so you better be more careful yet and more subtle.
But remember, you aren't going to change the narcissist. All you may achieve is to crack his facade. Nothing more.