Individuals with Cluster B personality disorders—including Borderline Personality Disorder (BPD), Narcissistic Personality Disorder (NPD), Histrionic Personality Disorder (HPD), and Antisocial Personality Disorder (ASPD)—are overrepresented among stalkers and harassers of former partners. A subset of these individuals not only persist in intrusive behaviors but also engage in mimetic identity disturbance: adopting the style, appearance, and behaviors of their ex-partner’s new romantic interest. Beyond this, some attempt to reshape their new romantic partner into a facsimile of their ex, recreating lost dynamics. These behaviors reflect profound identity diffusion, unstable attachment, and neurobiological dysregulation in frontolimbic, dopaminergic, and mirror-neuron systems. Victims of such dynamics often experience trauma, identity violation, and boundary collapse. This paper integrates neuroscience, clinical psychology, and forensic evidence to analyze the dual dynamics of mimicry and partner re-creation, and outlines therapeutic and legal responses.