Elegy of Emptiness

The "Elegy of Emptiness" is a song featured in Majora's Mask.

Learning Location
Played on the Ocarina of Time, it is taught by the King of Ikana in Ikana Castle after Link defeats him.

Uses
The "Elegy of Emptiness" leaves an exact replica of the form Link is in at the time, but it can only make one of each form. It is required to scale up the Stone Tower, and it's also necessary to solve several puzzles inside the Stone Tower Temple.

A total of four replicas can exist at any given time, one of each of Link's forms. The Deku form is the least used, however, as it is too light to be of any use, while the Goron replica is specifically used to press down switches that are bigger than usual. It is important to note that the replicas can only be formed if Link is in any of the areas pertaining to Ikana Canyon, for if the song is played anywhere else, it won't have any effect.

The replicas that Link's Goron and Zora form leave are that of Darmani and Mikau, respectively.

Etymology
An elegy is a mournful, melancholic or plaintive poem, especially a funeral song or a lament for the dead.