Two short tales survive which associate Mongán with the otherworld, both dating from the late 10th or early 11th century [REF].
The second, Tucait Baili Mongáin ("What caused Mongán's Frenzy"), is said to take place in the year in which Ciarán of Clonmacnoise died and Diarmait mac Cerbaill became King of Tara following the death of Túathal Máelgarb, events dated to the 540s.