An unnamed Remnant is the Remnant responsible for the events that happened throughout Mortal Coil. It has possessed a lot of characters in the books and believes in the destruction of the world by Darquesse will come to pass and will do anything to put her on the path to destruction. It was destroyed by Darquesse in The Dying of the Light.
The Remnant was captured by Billy-Ray Sanguine in the Midnight Hotel using the soul catcher he had stolen from the Necromancers. It was then brought to Serpine's castle where it possessed Kenspeckle Grouse so Dreylan Scarab could make him fix and make another Desolation Engine. It was then given a captured Tanith as a "gift" and tortured her by nailing her body to a chair in several different places. It was finally driven from Kenspeckle after China used symbols and captured again in the Soul Catcher.
The Soul Catcher was then returned to Solomon Wreath on the promise that he would return the Remnant to the Midnight Hotel after studying it.
Wreath was ordered by Auron Tenebrae to use the Remnant to possess Finbar Wrong to see if Valkyrie Cain would be the new Death Bringer. He successfully used the Remnant to possess Wrong and ordered it to see what would become of Valkyrie. The Remnant, seeing that Valkyrie would destroy the world as Darquesse, got excited and started to put together a plan. It tried to possess Wreath but he managed to escape by diving through Finbar's window in his tattoo parlour. On St. Stephen's Day, when the Midnight Hotel appeared in Ireland, the Remnant left Finbar's body as bait and lured in Anton Shudder who was soon possessed. Possessing Shudder, it returned to the Hotel where it released the rest of the Remnants who took over a club that Valkyrie and Fletcher had visited. It encountered Tesseract in Roarhaven soon after and after the Russian broke Shudder's arm, the Remnant abandoned him and possessed Tesseract by climbing in through the eyeholes of his mask.
It is later seen enjoying the chaos that Darquesse is creating when a Remnant had attempted to possess her; however, it is forced to leave Tesseract's body, along with the rest of the Remnants, so Skulduggery would not shoot Valkyrie. The Receptacle was activated, and most of the Remnants were sucked into the orb. The Leader refused to give in and while clinging on to Tesseract's coat it leapt and forced its momentum to possess Tanith. It then started to go after Valkyrie and heavily beat her until It was forced to flee when Skulduggery Pleasant fired his gun at it.
Near the end of the book it was encountered talking to Valkyrie's parents through Tanith and was also seen to be with Sanguine and kissed him. This left Valkyrie in shock as the pair both disappeared.
The Remnant has the ability to possess people, becoming capable os using any of their intelligence, memories, and abilities. When the Remnant is serious in a fight, it's host's veins will stick out, and their lips will glow black, which gives it access to it's full power, including increases strength and speed.