The urban legend that a serial killer prowls the woods surrounding Willowbrook, a favorite of Sage and her friends, is a motif that connects The Dual Nature of Imagination. Eddie takes advantage of the legend of Cropsey to conceal his own murders outside of the facility; the myth of Cropsey makes the existence of an actual serial killer seem less likely. The urban legend seems so outlandish that Sage discounts her own intuition about Eddie repeatedly, dismissing it as foolish.

Cropsey is also a metaphor for the ugliness of human nature. Eddie is allowed to kill and continue killing largely because of Willowbrook’s desire to hide the mistreatment and neglect of its residents. References to the mythical Cropsey are regularly contrasted to the everyday evils at Willowbrook.

At the same time, the novel perpetuates the harmful stereotype of the mentally ill serial killer, a trope that results from societal fears of people with cognitive disabilities. This stigma allowed institutions like Willowbrook to continue in real life, even after their abuses and/or neglect became known.