Two hellhounds appear in the series, Deputy Jordan Parrish and Halwyn.
In Season 3, Jordan Parrish arrives in Beacon Hills to join the Beacon Hills Sheriff's department. Parrish later learns he is supernatural and was in truth, drawn to the town via the Nemeton and his hellhound nature. In Season 6, Halwyn is whom built the closed unit in Eichen House back in 1912, and is tracking an ancient evil, the Anuk-Ite that escaped the Wild Hunt.
Hellhounds are initially amortal spirits who inhabit a living or deceased human host on Earth, giving life to the shapeshifter. They have the power of thermokinesis and pyrokinesis, and produce flames from their physical form.
They are also participants of the wild hunt, alongside and can be command of the spectral Ghost Riders.
A hellhound's eyes glow the colour of fire when they activate their powers or their supernatural alter-ego comes forth. When they under the command of a ghost rider, riding the wild hunt, their eyes and flames will glow the colour of teal.
They are also death omens, giving them psychic connections with other harbingers of death.
Nature & Personality
The hellhound is called as "Guardian of the Supernatural". They are instinctively driven to safeguard various elements of the supernatural world, such as supernatural locations of massive power, the secrecy of the supernatural as well as the creatures and beings that inhabit that world.
In Season 5, Beacon Hills is being terrorized by the para-scientists: the Dread Doctors. The Doctors genetically convert teenagers into imitiations of supernatural creatures, Chimeras. Parrish's hellhound side manifests out having a seemingly instnctive reaction to these creatures' existence. As the Chimeras are killed off, Parrish instinctively abducts and takes their paranormal corpses to the Nemeton.
Lydia surmises that because of the corpses' shapeshifted features, Parrish is keeping the secret of the supernatural safe from the general population.
In Season 5B, Parrish is repeatedly shown to be in conflict with and have instinctively become a foe of La Bete du Gevaudan after the legendary vicious werewolf is resurrected by the Doctors.
The hellhound is naturally impervious to fire itself, even in their human guises, though the human side still feels the pain of fire before they can trigger their true nature.
Deputy Jordan Parrish was enveloped in the explosion of a makeshift bomb but survived walking away, unscathed. In Perishable, he was soaked in gasoline then set aflame: his entire frame was completely unharmed, even his hair and fingernails.
A hellhound wields pyrokinesis: they can summon, generate flames or extreme heat energy from within their own body of their own will without harming themselves.
Fire also seems to be a part of the hellhound's physiology. In Creatures of the Night, Parrish gave off smoke from his wounds whilst healing from a massive injury. When Parrish shows his 'Beta' hellhound shape: his body displays fissures secreting lava upon his skin that appear like cracks on a volcano
Main article: Death Omens
The hellhound is known to be a Bearer of Death. Deputy Parrish has shown to be able to track down dead Chimeras, easily and swiftly pinpointing their location.
He is strong enough to flip Stiles' Jeep and to bend the heated bars of a jail cell
Lydia found a book that described a mythical Hellhound:
“Woden’s Hunt, also known as the Wild Ride or Wild Hunt. A myth of devilish riders in the sky accompanied by black dogs, spectral beasts whose eyes glowed with fire... A Bearer of Death and Guardian of the Supernatural, the black dog is also known by its more common name, the Hellhound."