Universal Studios Hollywood already does the Halloween Horror Nights haunted mazes, using properties light Stranger Things, and until they find a way to pull off a Triwizard Maze, a nightly light show that focuses on the monsters and other dark creatures of Harry Potter would be perfect for that section of the park.
While Harry Potter is something that is fun for the whole family, sometimes something a little scary can still be fun.
I certainly have to wonder if Dark Arts at Hogwarts Castle is meant to be a precursor to some sort of major Halloween event at the park.