The men and women of The Otherworld, including Elena Michaels, live in a world where the supernatural stays hidden from humanity as a whole. Of all the various monsters and evils that threaten this world, these rank among the worst.
- Stolen: Tyrone Winsloe is a rich "gamer" who enjoys capturing and torturing supernatural beings for experiments. Obsessed with his own twisted ideas of fun, Winsloe also runs a game where supernaturals are captured and released on his grounds so he can personally hunt them down with vicious hounds. Obsessed with the werewolf Elena, Winsloe attempts to force her to kill an innocent man, even threatening to have her gang-raped should she refuse.
- Haunted: The Nix is the most vile of the Nixen and one of the worst chaos demons in existence. Not content with just tempting mortals to evil, the Nix discovered a way to possess women and allow them to go on murder sprees, even being responsible for the crimes of Lizzie Borden. The Nix has a special love for murdering children and frequently leaves her hosts to take the blame for their murders before starting again. Gaining a hatred of the ghost Eve Levine for hunting her, the Nix tries to cause a school shooting in the high school of Eve's daughter Savannah. A monster who intends to continue killing forever, the Nix later tries to possess Savannah and cause her kill her adoptive parents just to spite Eve.
- No Humans Involved: May Donovan is an attorney and the secret leader of a dark cult that focuses on Human Sacrifice for power. Leading them to multiple murders and even having a potentially disloyal members killed while framing others, May even sacrifices children and binds their suffering souls for her own power while leading an attempt to sacrifice supernatural beings to enhance herself even further.
- Frostbitten: Travis Tesler is a sadistic werewolf. A voracious sexual predator who admits he doesn't like consenting women, Tesler tortures, rapes, and kills women and has done so all across Europe. Planning to bring his and his brother's illegal gunrunning operation to America, Tesler starts his killing spree anew and intends to wipe out the pack which stand in his way and allow his men to run rampant on the population of Alaska. Torturing an old man to death after viewing him as a threat, Tesler also tries to corrupt the man's mentally ill grandson into evil. Gaining an obsession with heroine Elena, Tesler tries to rape her and when she rejects his advances, he leaves her to be eaten by wendigos.
- Spellbound & Thirteen: Giles Reyes, real name Gilles de Rais, was a Serial Killer of children with a legacy of evil that spans centuries in his quest for immortality. Giles has for centuries experimented on supernaturals in ghastly ways and has gone onto inspire countless other killers and monsters in the series into following in his footsteps. Leading a movement for supernatural rights, Giles launches terrorist attacks against humans which take the lives of dozens. In his grandest plan, Giles has innocents tortured and killed to create a virus that will turn humans supernatural with mass casualties while testing it on members of his organization with no regard to the mass deaths that occur. Seeking to enslave even Lucifer, Giles tries to capture the devil's heavily pregnant daughter Hope Adams and murder her and the unborn child should Lucifer not bow and assist him with spreading the virus over the world so he may rule it. One of the most evil monsters to ever inhabit The Otherworld, Giles is feared throughout it for his legacy of evil and even long after his demise, his evil lives on in surviving members of his organization who continue to pose a threat to the world at large.
- Malcolm Danvers is a vicious and power-hungry werewolf and Jeremy's abusive father. When Jeremy became alpha, Malcolm left the pack rather than be ruled by his son, and reemerged after his assumed death, as the orchestrator behind the mutt uprising, using Santos and other proxies into recruiting psychopaths, killers and rapists in a bid to destroy his son's pack, resulting in the murders of several innocent people and Jeremy's pack members. Malcolm also stalks Elena and has her former pedophile stalker Victor Olson turned and has him show up at an art gallery to torment her. After the battle between the mutts and the pack ends with all the mutts being killed, Malcolm shows no regard nor care for their deaths, letting them kill Santos. Malcolm confronts Jeremy about his true intentions on continuing this war, taking Elena for himself; kidnaps Logan's pregnant girlfriend Rachel; and leaves the decapitated head of Elena's boyfriend Phillip for her to find. He claims his reasoning for the latter is to punish Elena for wanting to have a human life, going as far as to tell her that she should be grateful. Finding himself stalked by Alister, Malcolm goes on the run, leaving his followers to die, and killing a kind old man who gave him a ride. It's also revealed that he tried to kill Clayton as a child, being the werewolf who bit him, and killed Clayton's mother that same night, resulting in his father committing suicide.
- Thomas LeBlanc is a deranged misogynistic Serial Killer and Serial Rapist, who kept a scrapbook of his previous exploits complete with parts of his victims. When recruited into the mutts, he takes part in an ambush in which he stabs Jeremy with a poisoned blade that nearly kills him before Elena breaks LeBlanc's wrist while interrogating him for the antidote. Forming a petty vendetta towards Elena, LeBlanc attempts to murder her, managing to shoot and wound her while playing a cat and mouse game and callously killing a woman he mistook for Elena. Later when Amber demands to be turned into a werewolf, LeBlanc bites her and watches with amusement as she goes through a slow and painful botched transformation; while seemingly kills her, it's later revealed she's reduced to a vegetative state Later he has fun chasing down and trying to kill Logan's pregnant girlfriend, and when the time comes to attack Stonehaven, defies orders to keep Elena alive, intending her to be the first in a new scrapbook he's planning. A deviant who admits to having no morals, openly disdains and disrespects even his own allies, his habits and attitude crosses enough lines that one of his bosses, Karl Marsten decides to help Elena kill him when he's decides that he's had enough of LeBlanc.
- Clara Sullivan was once a rebellious young witch, and spiteful from her youth. While she had a moment of humanity in her past where she delivered and rescued a newborn baby from death, despite knowing the prophecies as a child growing up to be the Destroyer, she would later use this act later in life for more nefarious purposes. Having her magic stripped away as punishment for using it to kill people, Clara would later track this child Alister down and reveal his destiny to him, planning to bring about the Undoing—an event that would kill every witch on the planet—out of revenge. With Clara acting as Alister's hidden partner and mentor, Alister embraces his destiny, gaining a cult and army, entailing mass murder, torture, experimentation and brainwashing on numerous people at his hands. Clara has Alister seduce women to find a body for Clara to possess, if not destroying the souls of the victims, trapping them in their own subconscious. Clara wants the body of 12-year-old Savannah in order to survive the Undoing as a conduit and take Savannah's powers for her own. When the time of the Undoing comes and an attempt to kill Alister starts to prevent it, Clara and Alister track down his mother Ruth to kill her, and when Savannah breaks free and tries to escape, Clara chases her down, gloating to her how she'll use her powers to cause havoc and promising to kill Savannah's friends in the pack.