Dark Mirror

Dark Mirror
Type	Offensive Magical Item
Fields	Light, Shadow, Summon
Cost	40 rupees

The Dark Mirror appears as a handheld mirror, with a varying design that always perturbs any who behold it. Looking directly and intently into this mirror will bring out the evil that dwells within a person, bringing it to life in the form of a shadowy clone, identical except colored entirely black, and with the most cruel intentions the original could ever possess. This evil clone will usually strive to kill its 'original' self--and the holder of the mirror, if the looker and the mirror are not one in the same. If this clone succeeds in its murderous plot, it will spread chaos and ill-intent throughout the land in the most efficient way it knows. The clone possess all the intelligence and capabilities of its original self. An unintelligent creature, or being who is already pure evil, cannot produce a clone through the Dark Mirror.

The Dark Mirror treasure canonically appears in the Zelda series, initially in Four Swords Adventures. More information about the canonical version of this treasure can likely be found on Zelda Wiki.