Have you looked up Borderline Personality Disorder?

The challenge tends to be that the person will use some things that are true and then create a story of their own choice often that they themselves begin to believe and because there is "something that is true" a person might believe them more.

Human beings are storytellers but for someone who is disordered, they go beyond just a story but need to create their own reality. These individuals live in a world of denial and if they can get someone to believe them it gives them a sense of power. They get so they know what kind of people to target too, usually they pick honest and empathetic caring people or people they know are naive.