The front facade of the Academy of Unseen Arts has the word "Gehenna" etched into the front. Gehenna was mentioned in the Hebrew Bible as the valley where children were sacrificed to fire. It is the closest description to a Jewish concept of Hell.
Nicholas Scratch calls Harvey "farm boy". This is most likely reference to Sabrina, The Teenage Witch (1996), in which Roland constantly refers to Harvey as "farm boy".
Second mention of Riverdale, this time a funeral home in the city
Ambrose is under house arrest at the Spellman house and can only leave to attend the Acadamy of Unseen Arts, but in this episide, he and Luke are walking through the woods when they encounter the 13 witches.
Bronson Pinchot's character Principal Hawthorne mentions "The Wizard of Oz" in this episode. In real life, Bronson has been a lifelong fan of the "Wizard of Oz" and was even head of his local chapter of the "Wizard of Oz" Fan Club.