These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Darkling, the Villain Protagonist of Nightlife, is, in Cal's words, "a nightmare for hire and the Last of His Kind." A mercenary banshee who is in it for money and kicks in equal measure, Darkling's a casual killer who sees murder as a way to relieve boredom. Signing on with the Auphe's plan to travel back in time and exterminate humanity in its infancy, Darkling bodyjacks protagonist Caliban "Cal" Leandros, and takes him on a road trip to Hell. He tries to kill Cal's brother Niko's girlfriend, Promise, hires a pair of werewolves to kill Cal's girlfriend Georgina, then kills the surviving werewolf when they fail. He feeds a captured mugger to Boggle in order to bribe him into attacking Niko, then tries to gun Niko down himself, burns down the shop of a fence who tried to rip him off, and is captured while trying to trigger the apocalypse. Unlike the Auphe, who are doing it to ensure the survival of their species, Darkling is in it for the thrill and the cash alone, and he remains a greedy, swaggering egomaniac to the end.
Hobgoblin, better known by all and sundry as Hob, is the oldest living puck, and may be the first of his kind. He's also a sociopathic conman and killer who gloats openly about being "the reason there's no honour among thieves." Orchestrating the events of Moonshine from behind the scenes, Hob arranges for the kidnapping of Georgina, and the werewolf cub, Slay, in order to ensure that Niko, Cal, and Slay's father Flay, will go along with his plans, which involve using a gypsy crown to mentally enslave everyone he comes across. When his agent, Caleb, outlives his utility Hob pins him to the floor with Spanish poniards, cuts out his heart and rams it between his teeth. He then kidnaps Niko and plans to drain him of all his blood in order to activate the crown, while using Georgina's psychic powers as source of energy. When Cal interferes, Hob makes a very deliberate attempt at cutting him to pieces, bragging that: "I can do this as long as it takes. Piece by piece, strip by strip, I'll have you down to dripping bones, and when I'm done draining your gifted girl, I'll beat her to death with what's left of you."
Sawney Beane, the main antagonist of Madhouse, is a Redcap Serial Killer resurrected after several hundred years dead. He quickly sets out on a killing spree, leaving his underground lair littered with the bodies of his victims. He assembles an army of revenants and impresses his own personality on them, leaving them mirror images of his own psychopathic mental state, and fills the sewers with corpses, including those of a pregnant woman and a little girl. When Niko and Cal try to stop him, Sawney skins their Boggle ally alive, boasting that her hide is filled with a mother's love and will keep him warm on cold nights. He has a particular interest in Cal whom he tries to devour alive because of his Auphe heritage. "Abide in me traveller. Special boy with with special taste. The taste of madness. The taste of me."
Ho Yay (or Bro Yay if you so desire). The three male main characters have the Fan Nickname of "The Holy Trinity of Hotness."
In Roadkill Cal compares his relationship with his brother Niko to Robin and Ishiah's. The difference being that Cal and Niko are both quite heterosexual, while Robin is...enthusiastically pansexual. Robin and Ishiah are lovers.