Dark Mirror

The Dark Mirror appears Legend of Zelda: Four Swords Adventures. Its an object that was stolen by Gannon, and he used it to create Dark Link. The mirror revives Dark Link whenever the four Links kill him, causing them to face him several times. Eventually, when the four Links battle Dark Link a final time, the Dark Mirror creates an unlimited number of clones of him, until its destroyed by Zelda, allowing Dark Link to be destroyed.

Manga
The Dark Mirror played a similar role in the Manga adaption of Four Swords Adventures. Dark Link was created using it, using its power he was also able to start a volcanic eruption. The Purple Link attempts to destroy pretending to by allied with Dark Link, but a bungling Tingle ruin his attempt. Like in the video game, the Dark Mirror revives Dark Link, although he's only killed once. Later, when the four Links fight Vaati, the Dark Mirror makes it impossible for him to die no matter how much damage he takes. Dark Link turns against Vaati and Gannon destroys the mirror, despite Vaati's warnings (which turned out to be true) that he would die if the Dark Mirro was destroyed.