He is encountered several times.
Dernaith is encountered by High Elf characters in the year 3434 fighting with the elvish host of the The Last Alliance of Elves and Men during the siege on the battle plain at Dagorlad at the end of the second age. Along with the other two Spears Megoril and Thelaron, he leads the advance outpost, but Thelaron is lost to a black rider.
Dernaith (Dor Amarth)
-  The Fates of the Damned