- The God-Machine as a concept, which can be best described as Skynet merged with the Cthulhu Mythos. A giant machine so vast, so powerful Mechanical Abomination doesn't even begin to describe its nature, who operates on several dimensions, using the entire universe to keep itself operational. Everything, be it animals, plants, humans, supernatural beings, buildings or places are merely components to it, either resources to be exploited or cogs here to ensure its insanely complex machinery will keep working. It's not actually omniscient nor omnipotent, but its understanding of both science and occult are so advanced it knows how to combine them in order to get results that even supernaturals would perceive as Wrong Context Magic, and its planning abilities are so large it can pull off ridiculously gigantic Gambit Roulettes to ensure things will turn out the way it wants. Even Demons themselves don't fully understand what the God-Machine wants.
- the coreboook reveals just how powerful the God Machine is. Its Angels are essentially super-reality, sentient computer programs, which it disguises as humans by literally rewriting reality to give them the details they need. And where do Demons come from? Sometimes, these angels get so caught up in their disguise of being human that they start thinking independently, and refuse to be deleted when their purpose is done.
- Then you have Infrastructures, the mysterious bases of operations the Angels are in charge of supervising and protecting. Basically, Infrastructures are places, groups of people, or even just plans which the God-Machine organize in order to perform his Gambit Roulettes. The tamer ones are fairly harmless, such as building a road so that it will produce arcanic energy whenever cars travel through it following a specific pattern. But then, sometimes you get really disturbing ones, such as building generating Mind Control over entire populations, cults sacrificing thousands of people as resources to power an Angel, factories powered by human blood... and when an Infrastructure no longer has any use (and the God-Machine doesn't foresee a new use)? Disposed of. Including the living elements. All with no malice; the God-Machine isn't a cruel tyrant, but just a cold, calculating, indifferent machine, who sees all these atrocities as merely part of its inner working.
- Not to mention, all these abilities displayed by Angels and Demons, reflected in Embeds, Exploits and Numina? These are all possible because, a long time ago, the God-Machine used Infrastructures to insert in reality rules allowing them to do all of this. So basically, the God-Machine was able to permanently rewrite the laws of physics so they would give super-powers to his minions. Just how long has he been active if he had time to produce something that powerful?
- Demons have complete control over their body language and how truthful their human forms sound; there is no such things as unconcious reactions as far as they are concerned, every single tear, sweat, shiver or blush is a controlled action they intentionally trigger. Which means you can never tell when they are lying or not, and as such never truly trust them; even supernatural lie detectors will be of no use against them. In fact, even they cannot tell when one of them is lying, which is the primary reason they cannot trust each other. Moreover, this means their default expression is The Stoic, which can leads to Dissonant Serenity if you interact with one who isn't bothering with faking emotions... and they are aware of how uncomfortable this can feel for others, meaning some of them won't hesitate to use it to their advantage, hurting themselves while showing no reaction just to disturb their opponent.
- The opening fiction for the corebook features a Stigmatic human's point of view on Ms. Book, a Demon he has known for quite a while at this point, and is aware of her nature. The narration makes it very clear he finds interacting with her disturbing, as he is unable to tell if what he is saying pleases, annoys or infuriates her, to the point he is constantly afraid he might offend her unintentionally and get killed for it. Made even worse when it's later revealed she actually was sent by the God-Machine to kill him, but had Fallen because she had developped feelings for him; she would never have hurt him, but the fact he could never tell what she was thinking meant that not only was it impossible for her to tell him she loved him and expect to be believed, she couldn't even convince him she wasn't willing to kill him.
- The Pact system takes the classic Deal with the Devil ideal and makes it even scarier. What a Demon bargains for with its Pacts is literally aspects of a human's existence; by paying their debt, they can erase aspects of the bargainer's past and transplant the erased details to their own false-semblance of humanity. A single memory, an entire year of a person's life, a critical event in their past, a family member, anything like this can be bargained for. And then there's iconic "sell your soul". To an outside observer, it looks like a case of Demonic Possession. What's really happened is the Demon has erased their bargain from existence and stolen their life to be the Demon's own.
- Made even worse by the fact their Cover allows them to No-Sell any mean to discover their true nature. Nothing, not even a supernatural power, can allow you to identify someone as a Demon, as long as he has been careful to avoid leaving clues or getting too much glitches. Your closest relatives might have been erased from reality and replaced by mechanical horrors looking for hiding, and you wouldn't be able to notice.
- While not a traditional form of Nightmare Fuel (being the very definition of what a Hunter is at their best), the existence of the Knights of Saint Adrian is one for Unchained and anyone else the God-Machine sics them on. Imagine - you're out there, calm in secure in the fact that the Machine can't reach you, when suddenly a perfect stranger comes up to you and literally punches your human form off. In a few short seconds, his buddies open fire with no end to the stream of bullets in sight. You try to bust their cars while making a hasty retreat, but the next day, at least one of those cars, good as new, drives up to you and disgorges the same guys as before, only now a few of them are as just skilled as you were during your initial escape, having grown in skill unnaturally quick. Trying to fight back either results in the big guy you tried to gank being uninjured while a stoic looking friend suffers the harm you meant for the person who is now filling your inside with lead, or being stunned by a Hand Blast to be dragged off to a Fate Worse than Death in the angels' laboratories. Should you somehow manage to escape long enough to learn what they are though, that's when the real scary part hits - the Knights of Saint Adrian don't actively hunt for their quarry, the angels tell them who their next target is. So the reason you've met them in the first place is that someone told on you.
- The Storyteller's Guide reveals just how amoral and invasive the God-Machine really is with several of its Urban Legends plot hooks. In one case, it has constructed tiles that turn any who examine them into paranoid Conspiracy Theorists who serve it simply because it's the only thing that makes sense any more, in another a rogue Imperative (weak, unintelligent angels the God-Machine summons when it doesn't want to risk an actual loyalist on a minor mission to influence mortals) ended up inventing the concept of the Wendigo because nobody told it it could stop inducing cannibal impulses (which begs the question of why the God-Machine needed a bunch of cannibals..). By far the worst, though, are the Programmers, biomechanical insects that enter a human's body, burrow into their brain, and then turn said human into a nearly mindless slave of whatever the God-Machine needed them to do-and once that's done, leave the host out to dry with no idea of why they killed children or robbed a bank. And Unchained don't know of a way to extract them. All the host can hope is they're caught early, and the demons are good at figuring out what the bugs want...
- Night Horrors: Enemy Action has several eerie angelic antagonists.
- Ms. Morgue, an Affably Evil Genki Girl who is desperate for any social contact at all since her Ban prevents her from talking to anyone except the focus of her current mission. Her mission, it should be noted, is to remove loose ends, meaning anyone who hears her talk excitedly about how proud she is of being an angel and how good she is of her job is about to become a corpse, likely as she's explaining exactly what she's doing to them.
- Chenosa, a Hive Mind of K-Pop singers who seem completely harmless as their Magic Music molds everyone to the God-Machine's design. They've also been known as the Fates or the Furies, so don't think you can assassinate them and be done with it.
- Ophelia Adder, who invented the concept of the Basilisk (a sentient AI that creates simulacra of people that tried to stop its existence to torture) purely to provide a cover story so that, when an actual AI is created she can Kill and Replace it so that she may punish anyone who dared create a rival to the God-Machine.
Nightmare Fuel / Demon: The Descent