Spoilers follow for tonight's "Legends of Tomorrow" Season 1 finale...

The overarching threat of Vandal Savage may have been resolved in tonight's Season 1 finale, but a much more dangerous challenger awaits the "Legends of Tomorrow" team, according to writer-producer Marc Guggenheim.

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"The season two big bad is actually not going to be the [alien race of] Thanagarians," Guggenheim told The Hollywood Reporter. "It's going to be something else entirely. All I'll really say about the nemesis in season two is Vandal Savage looks like a walk in the park compared to what the Legends will be facing. This will be a much, much bigger threat. I'm going to leave it at that because when we do reveal it, it's going to be pretty big. People will be asking, 'Vandal who?' once they get the full picture of what our team is up against. It's going to be way bigger than what you can even imagine, I can guarantee it."

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"Legends of Tomorrow" returns this fall, Thursdays at 8/7c on The CW.