They have the ability to send a small wave of energy which will cause anyone effected to believe they are dreaming for a short time; after the effects have worn off, a person is immune to further effects of this for a moderate time.
They have the ability to make someone think they are seeing their worst nightmares brought to life for a short time; attempting to scare them into not attacking.
They can meditate in order to speed up their rate of healing; they are constantly drained while they do this.
Dream nymphs can speak to people in their dreams
Dream nymphs can enter a person's dream, but the longer they remain in the dream, the more it drains them of their energy.
Dream nymphs can cause someone who is asleep to have a nightmare.
Dream nymphs can slightly control dreams
Dream nymphs can see into peoples dreams whilst they sleep
As they are nymphs they do not age, remaining eternally young.
They have a telepathic/empathetic connection with nature and other nymphs
Dream nymphs are nocturnal.
Dream nymphs like to see into random people's dreams, and know their ambitions.
They are well adept at interpreting the dreams of others.
They often tend to be day dreamers, with their heads always in the “clouds”.
Dream nymphs would most likely be created or turned into one, by one of the oneiroi.