When Link first makes his way up Death Mountain, he will encounter an old man who is lost in one of the caves. Escort the old man to safety and he will reward Link with a valuable gift-the Magic Mirror. Link can transport himself between the Dark and Light Worlds using the mirror. By gazing into it while in the Dark World, Link will envision himself in the Light World and will be drawn back into the realm from which he originally came."
The Magic Mirror is an item from A Link to the Past. It is an extremely useful item and essential to the plot of the game.
Location and Use
The Magic Mirror has the ability to warp Link when he is trapped within the Dark World back into the same spot in the Light World. A portal to the Dark World will remain wherever he entered the Light World from, until he returns to the Dark through that portal or by other means. If Link is teleported inside a wall or some other solid structure, he will immediately return to the Dark World.
Inside a dungeon, the Magic Mirror can warp Link to the entrance.