The first episode of part 4 is titled "The Eldritch Dark," so it seems we'll learn as soon as the part 4 premiere just what unnatural alien havoc Blackwood has wreaked upon Greendale. He's on a mission to destroy Sabrina and her aunts, and he'll take the whole world down with him if he has to. But even he may be unprepared for what the egg monster will do. If part 3 showed us anything, it's that there's a much bigger world beyond just our dear Church of Night coven, Blackwood, and the Spellmans. The first indication was part three's pagan witches, who tried to resurrect their own almighty gods and now there's a time monster who may answer to no one, not even Blackwood. He may just find himself in need of all his former witch friends if he's to survive whatever he just brought into this world.