* CompleteMonster: [[ThoseWackyNazis William "Willi" Borden]] is the most evil user of the Ability in the story, who values his sadistic fun above all else. Once an [[StateSec SS]] officer named Wilhelm von Borchert, he was the infamous "Oberst" who [[MindRape traumatized]] Saul Laski by forcing him to commit murder. Borchert ordered the deaths of thousands in UsefulNotes/WorldWarII, and would regularly host "games" where hundreds of concentration camp prisoners were routinely sacrificed as pawns in a [[HumanChess life-size chess board]]. Upon reinventing himself as Borden, he created an annual game alongside fellow Ability-users that revolved around committing the most heinous actions to gain "points". Borden created serial killers, family annihilators, and terrorists to rack up the most points, and when he gets bored of such small stakes, he tries to take over the Island Club so as to play his "game" using entire countries as pawns in a world-wide war. Borden tortures, rapes, and kills dozens more innocents in his way to achieve his goals, and betrays multiple allies the second it conveniences him to do so.
* NightmareFuel: Quite a few, from Saul's tale to the hunting game on the island.
** The Ability itself. It is the power to control minds, tailored solely to dominating other human beings. The mind vampire simply overwhelms the target's mind and forces them to do whatever they desire. The victim is [[AndIMustScream fully conscious of what is happening]], but they cannot resist. In fact, fighting off the Ability is ''impossible''; if you are not one of the ''very'' few people who has either the Ability or some natural resistance, the best you can do is briefly hold off the psychic assault before the mind vampire inevitably takes control. Having the Ability is also apparently genetically linked to [[TheSociopath cold-blooded, psychopathic amorality]], and its wielders are all [[BadPowersBadPeople vicious human predators]] who ruin lives and kill people the same way they might crush an insect.
** "Cat's paws," Melanie's term for the people conditioned into permanent service with the Ability. Their minds are systematically destroyed and replaced with their User's will, leaving behind only what the mind vampire finds useful. This results in near-total and irreversible DeathOfPersonality, and what's left is little more than an animal at best. At worst, the victims become nothing but meat puppets for their User; their minds are ''gone'', and they can't even move or sense their surroundings without being Used. There's nothing left to do for people in this state except to [[MercyKill send their souls where their minds have already gone]].