The Black Figures were the main antagonists of the Are You Afraid of the Dark? episode "The Tale of the Super Specs".
Weeds and his girlfriend Marybeth, the protagonists of the episode, buy special glasses called Super Specs from Sardo's Magic Shop. Weeds accidentally casts a spell on the Super Specs, and from that moment, every time Marybeth puts the glasses on she sees faceless black humanoids and a hooded woman dressed in black pointing her. She tries to get rid of the Super Specs, but the glasses always return. When Mr. Sardo explains her that the glasses opened a window to another dimension where the black figures live, she asks him to help her and Weeds to close the portal. Sardo holds a seance and the black figures apparently vanish, but then a mysterious entity tells Sardo and the kids that two universes can't exist on the same plane, and that balance must be restored. Then, in Marybeth's house, the woman dressed in black informs two alter-egos of Weeds and Marybeth that the black figures were trying to get rid of our universe, too, and they did. The episode ends with the real Weeds and Marybeth, Sardo and presumably the rest of our universe trapped in darkness. It's unknown what happened to them.
The Black Figures from this episode are very similar to the Shadow People from folklore, that are also told by some to live in a parallel universe.