"It's called the Silver Mirror. It's a fae artifact, around ten or so feet tall. It's connected to all the reflections of this realm. It can reveal the truth and dispel illusions. Since it's made of Sun and Shade, it can cut the Darkness or Light out of a person's heart."

Despite the fact that Strange is describing this in terms that are honestly a bit vague, he's downright serious about the power of the Mirror and what it can do.