Crystal

Crystals are reappearing items in the Legend of Zelda series. The purposes of the crystals varies widely among the different games, although mostly used as a cage.

Zelda II: The Adventure of Link
Crystals make their first appearance in The Adventure of Link. Impa, Princess Zelda's nursemaid, gives Link six crystals which must be placed in the foreheads of six statues, each hidden in a different palace in Hyrule. Once all six crystals are in place, the entrance to the Great Palace opens for him, enabling him to reach the Triforce of Courage.

The Legend of Zelda: A Link to the Past
In A Link to the Past, the Seven Maidens, descendants of the Sages that originally sealed Ganon away, have been kidnapped and sealed in crystal prisons by the evil Agahnim. In order to free them, Link must defeat the bosses of the Dark World's seven dungeons. Once he assembles all of the imprisoned maidens, they combine their powers to remove the barrier on Ganon's Tower.

The Legend of Zelda: Ocarina of Time and ''The Legend of Zelda: Majora's Mask
Crystals have the same function in both Ocarina of Time and Majora's Mask. Here, crystals can be used to warp Link out of a completed dungeon. Also, nearing the end of Ocarina of Time, Princess Zelda is held hostage in a pink crystal.

The Legend of Zelda: Oracle of Seasons
Another appearance of crystals is in Oracle of Seasons. After General Onox kidnaps Din, the Oracle of Seasons, he imprisons her within a crystal. During the battle with General Onox, he uses the imprisoned Din to attack Link. Link can repel her attacks with the Rod of Seasons. However if Link strikes the crystal with any other attacks, Link himself would be injured.