The opening scene shows Sabrina changing outfits in front of a mirror, using her magics. This is a direct homage to the opening credits of the original show Sabrina the Teenage Witch.
The owner and bartender of the Gray room is Dorian Gray. Dorian Gray was an orphaned boy who was the heir to a great fortune. Basil Hallward paints his portrait, and Dorian declares that he would give his soul if he were always to be young and the painting instead would grow old.
When Father Blackwood introduces Aunt Zelda to the faculty members, all of their names are references to famous American writers of the turn on XX century, known for their supernatural and cosmic horror works. So, the teachers are Brother Machen (Arthur Machen, author of "The Terror" and "The House of Souls"), Brother Lovecraft (H.P. Lovecraft, of the Cthulhu Myhtos), Brother Bierce (Ambrose Bierce, famous for "The Devils Dictionary" and "An Inhabitant of Carcossa) and Sister Jackson (Shirley Jackson, "The Haunting of Hill House, among others). Blackwood himself is a reference to Algernon Blackwood, whose short tale "The Willows" is considered the forerunner of cosmic horror. The last teacher, Sister Carswell, is a reference to Carswell Prison, whose medical facility has a reputation for being haunted. The themes of these authors are constantly referenced through the second season.
During the Boil and Bubble challenge, Nick adds blood to the potion, stating "Cool it with newborn's blood, and the brew will be firm and good." This appears to be a reference to a scene in the play Macbeth. During the famous "Double, Double, Toil and Trouble/Fire burn and cauldron bubble" scene with the witches, the Second Witch adds ingredients to a cauldron and says "Cool it with a baboon's blood,/Then the charm is firm and good."
The scene in which the high priest and Sabrina have a battle against dates is a homage to The Omen 2: Damien