The myth/lore that I have heard about dopplegangers is that they are supernatural in a similar way to a vampire or werewolf since they were rumored to feed off the misery of loved ones around them. Thus, they often had a direct and calculated hand in the tragedies that often befell those around them. They always seek to be the center of attention to get the most spiritual energy at all times.
In fact, one could argue that being supernatural requires that your primary nourishment has to come from humans in some way. Vampires need blood, werewolves need flesh, and dopplegangers need spiritual energy which is often strongest longest lasting in misery and sorrow.
One could even argue that a Witches power comes directly from the imbalance caused from the supernatural creatures feeding off humans and is a dual feeder in a way as the requirements for their spells often require both a flesh component and a spiritual component.
If you take it further, the Hybrid is a dual feeder taking nourishment both from blood and flesh.
A ghost is a dual feeder taking from spiritual energy and material energy in the form of an anchor..
And, if following these lines there is probably a supernatural being that feeds on all the human fuels and combined with the balancing powers of a witch in their corrupted forms...maybe a lich?