The Nightmare are enemies that player encounters during the Underworld Dreams quest.
Strategy[]
Upon close distance will teleport to your location and will attack you as they teleport away. They will repeat this until either player is dead or walks away far away from them.
Weakness[]
Can't reach player while they kneel down. So it advice to kneel down and attack where they about to appear. Usually they can be killed with one hit if players level up their power.