Brandigan was the site of an extremely perilous adventure called the Joy of the Court, supervised by Evrain’s nephew Mabonagrain, and Evrain tried to dissuade Erec from assuming the adventure. Erec, however, took on the quest and proved victorious. Afterwards, Evrain threw a celebration in his honor.
At the same time, there's no indication that he was among Arthur's vassals, or needed to be, seeing that the strength and self-sufficiency of his island fortress (possibly an outpost of the Otherworld) would reportedly have defied anybody's siege. His name may be a variation of Yvain or Urien.
Evrain the Cruel
A sorcerer who, with his brother Mabon, entered Wales and laid waste to the city of Snowdon, ruled by Queen Esmeree the Blonde, whom they turned into a snake. He was defeated in combat and was put to flight by Gawaine’s son Guinglain.