Nightmares are creatures in 2012 animated film, Rise of the Guardians.
Background[]
Nightmares were made from the dream sand corrupted by Pitch Black from the dreams created by Sandy (The Sandman). They appear loyal to Pitch, feeding off the fear from other children. However at the end of the film, the Nightmares attack their creator, who is afraid of how the Guardians defeated him, showing that they potentially are loyal to no one but fear itself, attacking anyone who is either good or bad with sense of fear.