The versions have different accounts of how this came about, all of which agree that some form of bargain was struck whereby Fiachnae's life was saved by Manannán in return for a night with Cáintigern.
An early version of this tale is found in the Immram Brain where Manannán prophecies Mongán's birth and near divine nature to Bran.
[2] Mongán's ability to change his shape is alluded to in the 9th century tale De Chophur in dá Muccado (The quarrel of the two swineherds), found in the Book of Leinster, which is one of the stories setting the scene for the Táin Bó Cuailnge.
[3] The Ulstermen ask Manannán to send Mongán to rule over them, but he remains in the otherworld for a further ten years, returning to Ulster when he is sixteen.
Although it seems as though they are in the house for only a short time, when they leave a year has passed, and they are now at Rath Mor, Mongán's home near modern Larne, 150 miles away.
[12] Austin Clarke's play The plot succeeds; a poetic pantomime (1950) is a comedy based on the tale of Mongán and Dub Lacha.
The record of Mongán's death in the Annals of Tigernach has him killed by a stone thrown by one Artúr son of Bicior, described as a Briton or perhaps, following Kuno Meyer's reading, a Pict.
Whitley Stokes translated it as follows:The wind blows cold over Islay;there are youths approaching in Kintyre:they will do a cruel deed thereby,they will slay Mongán, son of Fíachnae.