The whole concept of the Feast of Feasts. A woman is selected among the coven to become the queen, which is considered one of the greatest honors; she becomes the main course of the feast.
The result of the feast in the episode is even worse. After the feast is almost cancelled, Mildred, a witch crazed to become the queen, slits her own throat in front of the coven and they happily jump and start eating her body.
You can even see Mildred smiling as they eat her.
Unsurprisingly, the episode where Batibat torments the four Spellmans through nightmares has plenty of Nightmare Fuel. Sabrina gets married to Harvey, but then he lets his family shove her into an iron maiden while her friends scream obscenities at her for being a witch. Ambrose has to do an autopsy on his own body and then has to endure that autopsy from the other side, screaming for help and unable to move. Hilda finds a romantic partner, only to discover he's fixated on her because of her insecurity related to being Zelda's appendage - and makes that insecurity literal by sewing her and Zelda together. Zelda murders and cooks a child as the happy intro to her nightmare - then she has a psychological breakdown when the Devil rejects her food for Hilda's and kills her sister, only to find she's killed Hilda for good this time in a Tear Jerker twist.
When the characters chant "Hail Satan" and "Hail Judas". Not only it is scary enough per se due to their hailing evil characters- but it also resembles a crowd shouting "Heil Hitler".
The Soul Eater that lives in Limbo and eats the souls of dead humans who end up there. Made worse by the Fridge Horror that comes from Limbo being primarily a destination for unbaptized infants. Adults can run and attempt to hide from it, but infants are almost certainly consumed very quickly.
Harrowing, full stop. An extreme form of hazing practiced at the Academy of Unseen Arts, the practice involves simulating the events leading up to the deaths of the thirteen witches killed centuries ago in Greendale. This includes being shut up in a cell with malevolent spirits that psychologically torture many victims to the point of insanity, being forced to stare at the hanging tree while something recreates the sounds of your loved ones being killed behind you (with the implication that, if you turn around, it will tear you limb from limb), and finally actually being hanged from the tree. This process has apparently killed several children down through the years, and is supported by the High Priest Faustus Blackwood as a means of weeding out the weak.
The Holiday Special has Susie working as an elf for the local Santa Claus at a store. She's helping him clean up and admiring his amazingly life-like statues of children set up around the man's chair. The Santa tells of how he "makes each and every one of them myself." Susie is cleaning a face... when she sees a tear fall from the eye of the boy. It then blinks as Susie realizes "Santa" is a demon who has been turning innocent children into these "wax" figures... and she's next.
Fortunately Susie gets recused by Gryla who after welcoming Bartel's victims to her family performs a karmic act against Bartel by trapping him in wax as he had done to so many victims. Said victims were pleased to see this happened.
The lengths Satan goes to win his bet with Madame Satan over Sabrina's willingness to obey, culminating in making Salem deathly sick and forcing Sabrina to burn down the school as a show of loyalty (admittedly, he stops her before she sets the fire, but only at the last moment).
Most of the visions that the tarot reader (actually a disguised Madame Satan) gives the characters during their readings:
Sabrina helps Nick demonstrate a levitation spell during a talent show, only for the Weird Sisters to sabotage it and leave her floating into space, where she freezes to death.
Theo steals a spell from the Spellmans to become physically male, but due to botching it starts turning to wood. Hilda amputates an arm, only to find that his legs have changed too.
Roz agrees to surgery to restore her sight, but feeling guilty over her father getting his parishioners to pay for it decides to pay it forward by volunteering at a home for the blind... and meets a girl whose eyes were gouged out to give to Roz.
Harvey gets into an art school, but his joy is tampered by a creepy roommate, whose paintings are inspired by a Hell Gate in his closet which unleashes Lovecraftian monsters.
Zelda decides to come clean about Father Blackwood's daughter Leticia before their wedding. When she visits Dezmelda to collect Leticia, she discovers that the old crone has eaten the baby to absorb her youth.
Ambrose is convinced by Father Blackwood to kill his aunts and Sabrina.
Leviathan, Ambrose's familiar crawling inside of him and controlling him to kill the Anti-Pope.
The spell Father Blackwood uses on Zelda to turn her into a Stepford Smiler who obeys him without question. Even more horrifying when you consider the fact that the two were on their honeymoon, meaning there's little doubt that they slept together while she was in this condition.
The Dark Lord tricking Madam Satan into eating Adam's corpse and then forcing her to "clean her plate of the mortal" as punishment.
The Order of Innocents- a group of angelic witch hunters who torture, murder and kill Witches, all with a smile on their faces.
Hilda’s spider curse it starts with her getting a big pimple on her face. And when she pokes it baby spiders crawl out of the pus, and over the course of the show she turns more and more into a spider even developing Horror Hunger.
In the finale Hilda and Zelda have to kill their niece, who's basically their daughter rather than a niece by now, by slitting her throat and watching her bleed to death.
