The third ballad in Binneas nam Bàrd is "Laoidh an Amadain Mhòir."
This is another lyric from Leabhar na Féinne. About the tune I did not locate any commentary.
"Laoidh an Amadain Mhòir" has 62 verses total.
The melody is printed on page 21.

This Scottish Gaelic tale straddles mythologies, with one foot in the accounts of the Fianna, and the other foot in King Arthur's Camelot. The relation to the Arthurian mythology is regularly commented on by numerous published scholars. It isn't so much that there are names or place-names out of Wales or Camelot in the tale; but the plot and the content, about a promising young stranger -- "Fair Unknown" -- put to a series of tests, some of them magical, makes a striking parallel to, for example, the accounts about Sir Gawain.