Its really a funny story with Doppelgangers. They're supernatural when you understand the story. Nature created people who look like Amara in order to punish the extremely powerful witch Qetsiyah for creating the Immortality Spell. Qetsiyah is then forced to watch her true love - Silas - fall in love with his true love - Amara- over and over again.

I.e Stefan and Elena and Katherine.

So doppelgangers are definitely supernatural.

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?

I also recall an episode in season 1 where Alaric, Damon, and Elena go to the university where she did her research and talked to her assistant. If I remember right Elena brought up the idea of a Doppleganger and the assistant described it in a similar way as described above although with less emphasis on the spiritual energy feeding aspect. And, if I remember right there wasn't much of a discussion about that description by any of them after that. Given how much they like to talk about every detail regarding the supernatural it seems that the point was just ignored mostly. That would seem to suggest that if Elena does have a direct hand in engineering situations that cause great emotional energy that she may have intentially steered the conversion away from that subject even though she was the one who brought it up. It could indicate the Doppleganger has a slight mental influence over others to facilitate here emotional energy needs.

I thought that was season two, wasn't it when they went looking for answers about Werewolves...?

Typo, maybe? And......Elena isn't smart enough to engineer....well, any of this. Sorry, dear, but it's just the truth. "pats Elena on the head"

Run along now, and go be selfish and shortsighted some more, alrighty? Good girl. "sighs"

I miss Katherine. At least she was aware that she was a horrible person alot of the time. Elena....so self-righteous, even AFTER she had her little bro commit genocide. Which either makes me think she's a sociopath on the level of Amy from the book Gone Girl, or she's dumb as bricks (bless her heart). Dealer's choice. Started to rant there a little, didn't I? My bad. In my defence, the writer's HAVE made her irritating.

Interesting theory anyways, anon. Nice callback to a little remembered moment.