Death Mountain BGM
Upon entering Death Mountain, you'll be introduced to the foreboding Death Mountain BGM tune. Unlike the Underworld music which is mysterious, the Death Mountain music is downright dark and nefarious, reminding you how close you are to the great evil of Gannon.
The title comes from the Famicom 20th Anniversary - Original Sound Tracks, Vol.1 album. The song is track 8 in the NSF file.