Both dramas are a fantasy-romance in a historical universe.
Both leads have supernatural power and try to find a way to get ride of their curses to save their lives and finally be able to live a normal life with their beloved.
Scholar Who Walks the Night is one of my favorite dramas. It has many supernatural twists. Mirror of the Witch is about witchcraft and SWWTN is about vampires. Both ways, both are Sageuks in the "dark". If you love this drama, give Scholar Who Walks the Night a try!
