1) The four utilities (Water, Power, Gas and Phone) are all elementally-aligned mega-corporations engaged in a bitterly cold war with one another. Water (HydroNec) is functionally destroyed, and now basically just an order of assassins obsessed with purity. Gas (PetroNec) makes most of the golems (out of plastic) and war machines. Power (Necrogen) is a bunch of ineffectual kleptocrats sitting atop a vast pool of elemental slaves. Phone (Necrotel) used to be Post (Necromail) until an internal coup by the partisans of an intelligent crystal re-oriented their business. They still deliver the mail.
2) Despite being very precisely 9998 years old, most of Necrocarcerus' history is lost due to an event just referred to as the Incident that happened about 3,000 years ago. Anyone who predates that isn't talking about it, and the only thing that's certain is that there was a higher baseline of technology and magic pre-Incident, as well as a different standard language than Regular. Most of Necrocarcerus used to be one giant urban megalopolis, and the wilderness only really came back after the Incident. That's why the capital of Necrocarcerus is referred to as "Downtown".
3) People from our earth go to Necrocarcerus when they die. There are Christians, Muslims, Jews, Buddhists, atheists and everything else; cavemen and people from the 34th century. People who die on other planets in our future don't go there, only people who die on Earth. You can play yourself if you really want to, it doesn't matter to me.
4) Necrocarcerus has no "nature", and things like dogs, horses, deer, trees, rocks, etc. are crude copies created by the Guardians, who have never seen the originals, based on verbal descriptions and hand-drawn pictures by amnesiacs. It's not uncommon to find things like ancient artifacts with thick black outlines copied over from the original sketches. In general, the more like a children's scribble something looks, the older it is. A handful of later citizens who were formerly artists are responsible for most of Necrocarcerus looking "realistic", and you can tell who did what if you know its art history.
5) Necrocarcerus' sun is a giant light bulb screwed into the dome of the sky, and it has to be changed every thousand-odd years (by elementals employed by Power). The light doesn't kill vampires, though it does hurt them. Similarly, the "stars" are actually giant collections of giant glowing spiders who live on the dome and lay IOUN stone eggs. They move around a lot and are unfriendly.
6) The Guardians are kind of stupid and gullible, except for the handful that are pursuing malign alien motivations. The Guardians don't rule Necrocarcerus because they don't know how, though they've tried a couple of times and screwed it up. The Guardians don't know the purpose of Necrocarcerus because that part of the transmission was cut off, and they're not sure how to end Necrocarcerus because that part of the transmission was lost (or stolen, no one's sure). The Guardians are not entirely sure who the Creator is, except that it created them and must be obeyed. Guardians get smarter the longer they're around, but are still basically semi-sentient golem-like dopes at the end of the day. The Guardians don't have magic powers beyond what's available to other people, they just know how to create a few key kinds of installations that let them do the rest (incarnation temples, hylic manufactories, dream pyramids, posi-plants, etc.). They can make these out of basically any raw materials that are laying around, and they don't know how to teach other people how to build them.
7) The Association of Useful Citizens (AUC - the government of most of Necrocarcerus) is basically an autonomous bureaucracy that legitimises a huge number of petty warlords. Nobody is really "in charge", though a ton of people think they are. AUC's main source of power is that someone convinced most of the Guardians that AUC is the legitimate and correct government for Necrocarcerus, and so they control most of the Guardians' facilities. Otherwise, AUC is mostly a brand-name various tyrants franchise themselves.
5) Necrocarcerus' sun is a giant light bulb screwed into the dome of the sky, and it has to be changed every thousand-odd years (by elementals employed by Power). The light doesn't kill vampires, though it does hurt them. Similarly, the "stars" are actually giant collections of giant glowing spiders who live on the dome and lay IOUN stone eggs. They move around a lot and are unfriendly.
6) The Guardians are kind of stupid and gullible, except for the handful that are pursuing malign alien motivations. The Guardians don't rule Necrocarcerus because they don't know how, though they've tried a couple of times and screwed it up. The Guardians don't know the purpose of Necrocarcerus because that part of the transmission was cut off, and they're not sure how to end Necrocarcerus because that part of the transmission was lost (or stolen, no one's sure). The Guardians are not entirely sure who the Creator is, except that it created them and must be obeyed. Guardians get smarter the longer they're around, but are still basically semi-sentient golem-like dopes at the end of the day. The Guardians don't have magic powers beyond what's available to other people, they just know how to create a few key kinds of installations that let them do the rest (incarnation temples, hylic manufactories, dream pyramids, posi-plants, etc.). They can make these out of basically any raw materials that are laying around, and they don't know how to teach other people how to build them.
7) The Association of Useful Citizens (AUC - the government of most of Necrocarcerus) is basically an autonomous bureaucracy that legitimises a huge number of petty warlords. Nobody is really "in charge", though a ton of people think they are. AUC's main source of power is that someone convinced most of the Guardians that AUC is the legitimate and correct government for Necrocarcerus, and so they control most of the Guardians' facilities. Otherwise, AUC is mostly a brand-name various tyrants franchise themselves.
8) Every thinking thing produces brain juice which can be distilled into nepenthe. Usually the Guardians drain people's memories when they're first incarnated, but citizens continue to produce more brain juice as they continue to exist, so it would be theoretically possible to extract it and turn it into more nepenthe. The undead are basically creatures whose brain juice has been contaminated by Nega-Energy, making it crystallise and otherwise function weirdly (skeletons and the like have had theirs evaporated into a mist that follows them around). Without distillation, all drinking brain juice does is give you XP as you absorb fragments of habits, skills and memories. It's distillation that makes the actual memories available.
9) Everything in Necrocarcerus is made of one of two substances, or a mixture of the two: Hyle and Pneuma. Hyle is psychically inert matter, pneuma is psychically & magically active matter. Most non-living material objects are made of hyle - swords, tables, buildings, etc. So are most bodies, though brains are crafted from pneuma (greater or lesser amounts determines your degree of sentience). There are people called "dream smiths" who can create items entirely out of pneuma in their dreams, but they're mostly imprisoned by the government and used for nefarious purposes, with teams of artisans being psychically projected into their minds to create complex horrors that can be then extracted back into Necrocarcerus. The most common origin of non-undead, non-golemic monsters is someone dumping unused pneuma in the wilderness where animal-likes stumble across it and mutate.
10) There are portals to the living worlds all over the place. It's just most people don't know about them, or how to use them, so they're at the mercy of whichever few happen to be open at a given time. The phone company mostly prevents them from opening & closes ones that are open because they interfere with cellular reception. Most of these portals open at best intermittently, or require rare keys, etc. Also, most folks are loosely aware that if you jump through a portal without proper preparation (whatever that means), you can only stick around in the living worlds for a short while before you're sucked back into Necrocarcerus.
9) Everything in Necrocarcerus is made of one of two substances, or a mixture of the two: Hyle and Pneuma. Hyle is psychically inert matter, pneuma is psychically & magically active matter. Most non-living material objects are made of hyle - swords, tables, buildings, etc. So are most bodies, though brains are crafted from pneuma (greater or lesser amounts determines your degree of sentience). There are people called "dream smiths" who can create items entirely out of pneuma in their dreams, but they're mostly imprisoned by the government and used for nefarious purposes, with teams of artisans being psychically projected into their minds to create complex horrors that can be then extracted back into Necrocarcerus. The most common origin of non-undead, non-golemic monsters is someone dumping unused pneuma in the wilderness where animal-likes stumble across it and mutate.
10) There are portals to the living worlds all over the place. It's just most people don't know about them, or how to use them, so they're at the mercy of whichever few happen to be open at a given time. The phone company mostly prevents them from opening & closes ones that are open because they interfere with cellular reception. Most of these portals open at best intermittently, or require rare keys, etc. Also, most folks are loosely aware that if you jump through a portal without proper preparation (whatever that means), you can only stick around in the living worlds for a short while before you're sucked back into Necrocarcerus.