Ravio's Bracelet

Ravio's Bracelet is an item appearing in.

History
Link receives Ravio's Bracelet from Ravio as payment to stay at his house, as Ravio is unable to pay rent directly at the time. At first, the bracelet isn't activated and doesn't seem to have a purpose, but Ravio insists that it's a gift that Link should take.

Later, while trying to rescue Osfala from the Eastern Palace, Link encounters Yuga as he turns the Sage into a painting. Link engages Yuga in battle and initially seems to defeat him, but Yuga begrudgingly uses his power to turn Link into a painting on the wall, seemingly trapping Link forever. Soon after Yuga departs, however, the bracelet begins to glow from within the drawing, allowing Link to escape and return to normal. From then on, Link is capable of merging into walls at will.

When Link returns to his house to speak to Ravio, the latter is surprised to discover his bracelet's true power, and expresses interest in trying to gain its power for himself, though he immediately decides against it.

After Yuga is defeated, Princess Hilda uses the bracelet to send Link and Princess Zelda back to Hyrule. This utterly exhausts the power of the bracelet, causing it to shatter into light and disappear.

Uses
After being activated, Ravio's Bracelet allows Link to transform in and out of his painting form at will. As this one of the major mechanics of the game, used for everything from walking along walls to reach new areas to traveling between Hyrule and Lorule, Ravio's Bracelet is thus used constantly. It also plays a role in certain boss fights and allows Link to use the Bow of Light.

Theory
It is possible that Ravio was feigning ignorance when Link told him about the bracelet's power, and used it to intially enter Hyrule. While playing the game in Hero Mode, the Vacant House in Lorule (which corresponds to Link's House in Hyrule) contains a diary that mentions how "'she' wants to do the right thing," how 'he' is deceiving "her", and how the writer wants "save her" by "go[ing] 'there'", but may be unable to return afterward. These entries coincide with the events of the game's backstory, in which Hilda and Yuga conspired together to enter Hyrule and steal the Triforce and Ravio left to try to stop them, making it almost certain that Ravio wrote the diary. It is possible that he then used the bracelet's power to cross into Hyrule, thus exhausting it in the process. It is noteworthy, however, that Ravio somehow crossed back into Lorule after the final battle, and thus may be able to somehow move between the worlds without the bracelet.

How or where Ravio obtained the bracelet is never ascertained completely throughout the game; however, if Link visits Ravio after gaining the ability to wall merge, his dialogue suggests that the bracelet repowered itself by absorbing Yuga's magic in the Eastern Palace. Thus, it's possible the bracelet was originally created by Yuga, or possibly Hilda, and given to Ravio under the assumption that he, in Link's stead, would be the one to gather the portraits of the Seven Sages and obtain from them the Triforce of Courage. If this were the case, the bracelet's limited power could possibly have been drained when Ravio used it to pass from Lorule into Hyrule, as this would have taken place before the worlds were drawn closer together by Yuga's scheme, and Ravio would then have given it to Link in order to grant him protection against the sorcerer's powers.

Trivia

 * Prior to its activation, the hollow in the bracelet is empty; afterward, it contains what appears to be a purple gem or light.
 * Ravio remarks that he would be interested in using the bracelet to "steal Yuga's power," too. This remark seems to indicate that the bracelet received its power by absorbing Yuga's magic in the Eastern Palace.