Nightmare Hounds are ancient monsters whom named that way due to their dog-like appearance. They lived both to serve the Great One, Priestess of Ancient Religion, and the Priestess' most trusted underlings, acting as foot soldiers, guard dogs and/or assassins of those whom summoned them.
Nightmare Hounds was once live coexist with humanity during the golden age of Lemurian and Atlantis' civilazation alongside other Creatures of Darkness. However, after learned about The Great Old Ones' true nature and also their weaknesses, both civilazation began a revolution where they uses weapon that can banished, if not truly destroy all Great Old Ones as the cost of their great achievements. Nightmare Hounds also one of the banished Creatures of Darkness as well.
However, it doesn't mean that these monsters can never returned to the world, as they have power to returned under consent of Great One's trusted followers. Morganians have used the Hounds as their war dogs alongside several actual war dogs that turned into familiars, but it was said that only the trusted commanders of Morganians whom allowed by Priestess of Ancient Religion to command these hounds due to their loyalty to those whom opened the portal to our world for them. If a Morganian member defy this rule, the Priestess would personally punished the said member as those whom command Nightmare Hounds are highly dangerous.
The Hounds were occasionally appeared to our world to hunt down Balthazar Blake to failed his mission for Prime Merlinean, and their sightings apparently inspired the story of Hounds of Tindalos given to their habit to manifests through smoke concealed portal that opened through angled surfaces such as corners of a room.
Froma distance, Nightmare Hounds looked like a dogs, but upon closer inspection, they revealed to be skeletal in appearance, with the bones of extremities, tail, and upper snout exposed. They also have dull spikes proturding from their ribs. The hounds' eyes however, glows in purple, and in place of eyelids, the creature has silvery nictitating membranes that cover their eyes and protect them from harm. Should the Nightmare Hounds is killed, the light on the hounds' eyes would died out. Their blood is purple in color and pus-like.
While the beasts virtually the inspiration of Hounds of Tindalos, Nightmare hounds itself ironically had normal bluish tongue instead of long, hollow tongues or proboscis that can drain victims' body-fluids. Also, instead of suck their victims dried, Nightmare Hounds gains sustenance by killing their preys with sharp teeth so they can eat their flesh just like wolves on Earth. Eerily similar with Hounds of Tindalos in Frank Belknap Long's story, Nightmare Hounds can entered our world through portal that spewing forth smokes on any corner if it is fairly sharp—120° or less. However, the portal can only opened by a conjuror whom had Mark of Hound burned on his/her arm as the mark serves as formula to create portal that released the Hounds if channeled with his/her energy. Their senses, speed, stamina, and strength are crazily superior than regular war dogs in spite of their frail looks, making them the dangerous advesary to deal with.
- Nightmare Hounds are clearly inspired by monsters of the same name from Frank Belknap Long's story titled The Hounds of Tindalos. It was even clarified that how Frank got inspirations for Hounds of Tindalos was due to him saw a Nightmare Hounds materialized to the world when its pack chasing Balthazar.