Consider the Narcissist as pathetic and weak as he is. That is reality. Narcissists know they are inferior. Narcissists have a sense of themselves as weak and need to make up for their lacks by being sneaky and devious, and seeking to manipulate other people.
You might enter the relationship being made to feel a bit superior, then, somehow you find yourself being ground down, second guessing yourself, doubting your perceptions.
If you realise this feeling of disquiet has been created by the Narcissist, step back. Watch, predict his responses. For example, you suggest one thing, he takes the other. He begins to criticize what he previously commended.
As soon as you see this, as soon as he does exactly what you expect, laugh.
In short, once you no longer care, once their opinion means nothing to you, once you define yourself outside of the Narcissist, he loses and can not bear it.
Get away from the Narcissist, put people between you and him. Listen to them over him. Ignore him, no matter what he does, turn your back.
Nothing is more devastating to a Narcissist then when you turn your back.
And you escape.