Imposter

From the fumbling fool to the universally respected prodigy, every being suffers from moments of doubt when they believe all of their successes are due only to luck and that they will soon be revealed to be the frauds they are. Such thoughts usually pass quickly, but sometimes they can leave a psychic impression on the Astral Plane. When a creature’s lack of confidence returns again and again, these imprints grow strong enough to create a rare outsider known as an impostor—a creature that feeds on self-doubt.
An impostor takes on a form reminiscent of the creature whose doubt created it. However, it is a nightmarish, funhouse-mirror version of the creature, with an elongated face and hollow eyes. When an impostor is created, it can push its way onto the Material Plane, its only thought to end its progenitor’s life. As a creature born from the dark places of the mind, an impostor can manifest doubt as a weapon: a cold blade that seems to absorb light.
Once an impostor has finished off its creator, it seeks ways to undo their accomplishments. Though an impostor is rarely mistaken for its progenitor, it knows their every shameful secret and worst impulses, and it uses this knowledge to further its cruel agenda. Once it thoroughly spoils a person’s reputation, the impostor fades from existence, its energy returning to the Astral Plane.