Keeper Selentia

Keeper Selentia can be found in Shal'Aran in Suramar during the quest Arcane Thirst. She is invulnerable until the two Arcane Tethers are slain. She will also summon Ancient Keepers.

Speculation
Selentia is floating above a desiccated tree stump that crumbles away when she dies. It is possible that this was an early attempt at an Arcan'dor that did not fail as catastrophically as the one in Falanaar, which could make Selentia one of the order that trained Valewalker Farodin.