Dorocha

"They are the voices of the dead, my child. And like the dead, they are numberless."

- The Cailleach to Morgana

The Dorocha are voices of the dead who inhabit the Spirit World. They can kill a man with a single touch and are immune to magic.

History
In the time of the Old Religion, the High Priestesses would gather together on Samhain's Eve and perform a blood sacrifice. The sacrifice tore the veil between the worlds and released the Dorocha into the living world.

One year after her failed attempt to conquer Camelot, Morgana sought revenge by sacrificing her dying sister Morgause to tear the veil between the worlds. The Dorocha quickly spread throughout Camelot, devastating entire villages and leaving hundreds of citizens dead or displaced.

After Gaius determined that the only way to banish the Dorocha was to repair the veil, Arthur, Merlin, and the Knights of the Round Table traveled to the Isle of the Blessed to perform a second sacrifice. Arthur intended to offer himself for this purpose, but Lancelot stepped through the veil in his place, healing the tear and returning the Dorocha to the Spirit World (The Darkest Hour).

Abilities
The Dorocha are powerful creatures of magic who can kill any mortal with a single touch, seemingly by freezing them to death. When Merlin was touched by a Dorocha, his body became coated with frost. Conversely, Dorocha appear to be weak to warmth and light, as they can be repelled by fire and only come out at night.

The Dorocha are also known to be immune to magic. In fact, Merlin was unable to use his powers at all while in their presence (The Darkest Hour).

Trivia

 * It is unknown whether all humans become Dorocha after death (The Darkest Hour).