When Ganon Appears and Is Defeated Fanfare
The When Ganon Appears and Is Defeated Fanfare plays when Link makes his way through Death Mountain, finds his way to Gannon's lair, and hold the Triforce of Wisdom high above his head, beginning the final battle. It is played a second time when you defeat Ganon.
The title comes from the Famicom 20th Anniversary - Original Sound Tracks, Vol.1 album. The song is track 7 in the NSF file.