What does mysterious as the darkside of moon mean in Disney movie mulan?

In the Disney movie Mulan, the phrase "mysterious as the dark side of the moon" is used to describe the character of Mushu, a mischievous dragon who serves as Mulan's guardian. The dark side of the moon is often associated with mystery and intrigue, as it is the side of the moon that is not visible from Earth. This phrase suggests that Mushu is a complex and enigmatic character, full of secrets and surprises.