Darkworld. This is a definite. Not complete. I'd started this one a while back and I was trying to develop it as a stand-alone, but I changed my mind, so I'm putting it in the medley. This is one of my top favorite Zelda songs.
In case anyone cares, my top 5 Zelda songs:
5. Hyrule Field (Ocarina of Time)
4. Boss Battle (Majora's Mask)
3. Molgera (Wind Waker)
2. Darkworld (Link to the Past)
1. Morpheel/Argorok Battle (Twilight Princess; the song is the same in both battles, but the interludes are different.)