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Nightmare Fuel: Shadowrun
Shadowrun's Third Edition Cybertechnology sourcebook is a good source of this, particularly move-by-wire implants and cyberzombies. Both are revisited for Fourth Edition in Augmentation.
The move-by-wire system, like most reaction-enhancing 'ware, is a horrifically invasive implant, but MBW puts the body into a state of constant seizure and works with conscious muscle control to decrease signal latency, effectively giving the user superhumanly fast reflexes. The downsides are if the control unit is damaged, you have no conscious control over your body's movements and users typically develop temporal lobe epilepsy with complications (TLE-X), which persists even after removal of the implant. Symptoms include seizures (uncontrolled now) and mood and personality disorders. The only way to fix it? More invasive brain surgery. Yep, really good trade-off for that edge in combat, chummer!
Cyberzombies are metahumans implanted with more cybernetics than their essence can handle, with magic binding their souls to their now-dead bodies. The soul of the cyberzombie knows that it shouldn't be alive and that knowledge causes them to stop working on a cellular level without a horrific cocktail of obscure magic and medication. Even then, few last longer than a year before cancer and necrosis rots their bodies away and they're almost never even in the same time zone as sanity. A section of Cybertechnology follows the creation of a cyberzombie: the signature character Hatchetman.
On the magical side of things is the Blood Mage Gestalt in Aztlan (SR Mexico). At best, they are sacrificing hundreds if not thousands of people yearly "Aztec"-style to keep their President from parts unknown alive. At worst, it's to speed up the return of the Horrors from Earthdawn (see below) to our world. Usually, though, they just kill people to power-up their spells or to summon spirits into the world comprised of the blood of the sacrificed victims. These spirits would be more than happy to engulf and drown you in that blood, if their master orders it.
The spell Turn to Goo does Exactly What It Says on the Tin: it turns the subject into an amorphous homogenized mass for the duration of the spell, which is thankfully unconscious. This wouldn't be as big a deal if it turned the target entirely; it doesn't affect clothing, gear, or cyberware implants. A popular tactic is to turn a target into a puddle of snot and then pull out their implants before ending it. A Lot of popular implants are load-bearing like limbs, eyes, and nervous system augmentations.
Bug City. The Chicago sections of Real Cities is probably the most unnerving part.
Lockdown. Later books reveal Deus's semi-understandable motives for creating that hell, but that does everything but justify his actions for turning an entire miniature city into a game of System Shock with brainwashed slaves and Creepy Child cultists with Glowing Eyes of Doom all so he could live in the physical world.
The first metaplot arc in the Shadowrun universe concerned the Universal Brotherhood. The Brotherhood was a beacon of hope in a hopeless world, a charity that offered food, shelter, and medical care to the poor and SINless. Finally, someone's looking out for the little guy! It's too good to be true! It was. The Brotherhood was under the control of insect spirits, using it to gain hosts for more of their kind so they could invade the world.
In the real world, they tore down the Kowloon Walled City in the 1990s. In Shadowrun, the refugees from the Chinese Civil War rebuilt it. Now it's home to hundreds of thousands of people who have no way out, paying their rent to the Triads because the regular people don't dare go in. Kowloon itself isn't that nice, but the Walled City is so full of suffering and pain that the Yama Kings have manifested and are slowly grinding away at the souls of the people trapped there. The Universal Brotherhood tried to reach out to the people within, but the Yama Kings are so powerful and twisted that they consumed every insect spirit they can catch.
And then there's the Horrors. You see, there are these things from beyond any world that the human mind can understand, and they feed on pain and suffering. And even the weakest among them could take down a dozen men single-handedly. Thankfully, they are incapable of surviving without a great deal of ambient magic, so... oh. Wait. The world's magical potential has only risen since 2012. The last time they showed up, the only way any sentient life survived was burrowing into tightly-sealed chambers of magical earth. And that time, we knew they were coming.