When things go wrong in a narcissistic relationship, narcissists often engage in a smear campaign to damage their victim's reputation by spreading false information about them to others, making the victim look like the bad guy.
Image is everything to a narcissist. They care what people think about them—a lot. Should things go wrong with a narcissist, upholding their pristine image is of utmost importance to them. They must appear to be blameless; it's they who are the victims here. They thus deflect any perceptions of wrongdoing on their part, dragging their victims through the mud, thereby making themselves the innocent and wronged party. This is one way the narcissist shifts any focus away from their own shortcomings or role in the relationship's demise. (See projection.)
If you find yourself on the receiving end of a smear campaign, stay clear and don’t get into the mud with a narcissist. There’s an old saying: “Never wrestle with a pig. You both get dirty and the pig likes it.” In other words, when it comes to a narcissist, stay clear and stay clean.