Moon Pearl
The Moon Pearl is a shining gem which allows Link to retain his normal shape while in the Dark World. Other humans entering the Dark World are transformed into shapes which reflect their "True Nature", or personality. This is shown by the pair of men on Death Mountain, as well as Link himself. The bully is transformed into a demon-like creature because of his devilish nature, and the other man turned into a ball because he could never make up his mind. Link's "true nature" is apparently a cute little pink bunny rabbit, probably due to his kindness and compassion. (This is commonly referred to as Bunny Link.) This Pearl appears in A Link to the Past. Several Moon Pearls also appear in Four Swords Adventures. In that game, one pearl is sufficient to open one Moon Gate.