There are eight different Eldritch Terrors, all of which predate time and space itself. They are immortal, inhuman and world destroying entities. The first of these ancient beings is known as The Darkness. It is said to be all consuming, it wreaks havoc within wherever it decides to go.
When the darkness first appears, the voices of its first victims, miners of the Greendale mine can be heard. Telling of how it feels. It is said to be all consuming, suffocating, and crushing. It spreads everywhere, taking all light from the area. It starts with darkness and ends in darkness, there will be no light from the sun when it is finished.
When the spectral miners go within the town of Greendale each Spellman crosses them. The one who shows more of their power, in a way, is the one that crosses Zelda's path. It broadcasts her fears, her insecurities, everything she doesn't speak aloud and tries to use them against her. Until her sister, Hilda comes up with a candle, the mask of the miner is removed and the face is nothing but pure darkness. Then, it dematerialized leaving nothing but the clothes and pickaxe.
Mary Wardwell herself, comes across a miner. As she was working in her office she heard a crashing sound. Mary went to investigate and saw the miner destroying the light in the hall. When she moved back to her desk, her door was broken open by the miner. She remembers how Father Blackwood told her that even now the light can't save her and blows out her candle. With the miner being appeased it left.
Theo and Robin waited by the entrance to the mines to attract the next horde of miners that would come from the depths of the mines. Once they do, they lead them to the Phantasmagoria carnival. Which allowed both Sabrina’s and Ambrose to sneak into the mines to trap the darkness. While they were doing that Roz and Harvey led the miners deeper within the carnival with road flares. They dropped them in one of the tents as a distraction so Nick could trap them within it.
Once they were where they needed to be, Ambrose reminded Sabrina Spellman and Sabrina Morningstar that being exposed to the darkness for too long would ensure death. Death by despair as he put it. Sabrina Morningstar offered to go in and trap the darkness. But, instead of trapping the darkness within the lightbulb, she succumbed to her fears that she was shown by it. By telling her she is an unloved orphan. Sabrina Spellman decides to go in, and finds Sabrina Morningstar crying. And offers to help and reminds her, that they are loved.
But their power is not enough, their eyes begin to become completely black. And Ambrose calls on the coven to help the two of them. With the help of the coven both Sabrinas are able to access their Morningstar light, fully, and with the help of praying to Hecate they trap the darkness within the bulb.