Hell Spelunking Horror V3

It starts out as a mindless demon slaughtering FPS.
The opening scene is the totally buff player-character horse-riding a nuclear missile into space, allowing the player to choose any location on the surface; then riding it back down to Earth, throwing the missile ahead of them just before they land and punching their way through the explosion, and through roughly 100km of crust and mantle.
Landing in an empty space full of demons, the player then gets to mow down demons and similar abominations with a machine gun.

The only reason this seems to be what the game is at first is purely because of the region system.

"Region" refers to the 3 regional variables of any given point (Jargon explained later):

Demonic: Weights entities, scenes, and details towards being of a demonic type; weights, environments structures and their details towards being artificial, firey, demonic, and more open; increases the prevalence of aggressive behaviours, especially long-range pursuit; has more mundane items; and has more vehicles and structural features to aid movement.
The demonic regional variable is uniformly moderate at the starting ~100km depth, averages high at a ~1000km depth, then as deeper depths are reached the spherical layers taper off from fairly uniform into an ants-nest lattice of increasingly demonic regions (Though patches of wildly varying demon level exist outside this lattice).

Horror: Increases the prevalence of zero-lighting horizon spawns; weights entities, scenes, and details towards being of a horrific type; weights lighting towards darkness; increases the prevalence of aggressive behaviours, especially stalking; and has more arcane/powerful items.
Rather random distribution, with the average level increasing with depth.

Benevolent: Decreases the prevalence of anything demonic and horrific; increases the prevalence of anything mundane and idealistic; and weights lighting towards bright.
Sporadic distribution, less common with higher demonic and horror levels. If overlapping high demonic and/or horrific levels, then the area generates as purely benevolent, but details are altered over time towards demonic and/or horrific.


As for the unexplained jargon...

Metametanode: A few billion of these are scattered over the entire world, and these each generate (2 to 16)*(2 to 16)-1 metanodes around them. These weight what sentient entities are chosen by nodes, and what environments are chosen by metanodes. Metanodes often have a boss (An entity that is especially powerful and unique), and can have multiple bosses (An exponential increase in boss number means a linear increase in combined boss power. Boss power increases with the number of metanodes attached to the metametanode.).

Metanode: Distributed randomly around the parent metametanode, and can be literally anywhere just as long as it is not closer to an unrelated metametanode than it is to its parent metametanode, and keeps some distance from other metanodes (Metanodes will be culled if there is not enough room). These generate (2 to 16)*(2 to 16)-1 nodes each around them. These weight structures and environments of nodes.

Node: Same placement system as the metanode. Defines how the world is generated; the form, appearance, entities, and activity of any location are subject to the nearest nodes.
As their direct children, these contain, 0-2 lighting systems, and any number from zero-to-lots of different scenes, structures, and entities. All these selections are random, but weighted by various things such as region.

Environment: Biome and topology. So it could be a fiery cave, a permasunset beach, an icy place that has different times of day but is always snowing, a fertile and quenched landscape (This would have the environment create foliage and water bodies as structures); anything really.

Structure: Buildings (Such as a spiralling tower. Or groups of buildings, such as a mall- which would be more like a maul) and environmental features (Such as forests, or fiery pits; environmental structures are controlled by the environment).
These weight node entities; the three structures I mentioned are more likely (Any combination is possible though) to have horses, demons, and sentient beings (Including more demons) respectively.
Structures will also have their own entities, such as trees for forests and books for libraries.

Scene: A behaviour relating to 2 or more entities, or the structure and at least one entity.
Most scenes involving structures/structure entities only apply to particular structures.
A scene might be a lynching, a party, a quiet reading, a couple of towers being destroyed; anything programmed really. To choose the entities involved, each slot in the scene calls for entities with one or more particular attributes (Attributes can also act as weights rather than requirements), chosen randomly from either the node or from all entities in existence.
So for a lynching, the attribute requirements might be: something that can be used as a noose, weighted to be rope; something with arms to perform the lynching, weighted to be sentient; and any sort of creature. If a node with a lynching scene has humans, then humans will likely be selected to do the lynching, with the scene introducing a new entity being unlikely; if gorillas were in the scene instead, they may be chosen, but the scene would likely introduce a new entity due to gorillas lacking the sentience weight.

Lighting: There are four types of lighting: The two non-node types, environmental lighting (e.g. sun/moon/starlight from an illusory sky) and structural entity lighting (e.g. electric lights); and the two possessed by the node, ambient occlusion and player aurora.
Non-node is only affected by regional influences, whereas node lighting is affected by what lighting already exists; the more non-node lighting there is, the less likely node-possessed lighting will generate; so if there is no non-node lighting, there will very likely be node-possessed lighting (God forbid there isn't); and if there are both kinds of non-node lighting, it is unlikely that either type of node-possessed lighting will spawn, very unlikely that both will.

Zero-lighting horizon: A shape comprising the closest points around the player that have so little light passing through them, that if a perfectly white object appeared at the point, it would render as pitch black.
A direction in the zero-lighting horizon is only valid if that direction looks pitch black to the player. This means that anything that is on the invisibility horizon is pitch black against pitch black.
The zero-lighting horizon is calculated at random intervals, and the entities that spawn just outside it only have a chance of spawning instant after a calculation.
Said chance increases with horror level: No horror means no chance, very high horror makes a poorly lit area an even worse version of that one Doctor Who episode in that things keep on ''coming out'' of the shadows. The entities that spawn must be creatures of a kind, they are especially subject to regional weightings (So they're virtually all horrific), and they have a higher number of details than average.

Entities: An entity is something that spawns in a node, or as part of a scene/structure. It can be anything physical that isn't regarded as landscape or a large-scale structure; it can be a creature, a vehicle, a weapon, even a lightbulb. A node/structure will populate itself with as many of an entity it possesses as it likes; one definition does not mean one acting object.

Details: Any modifier that can be attached to an entity or structures (Not all details are compatible with all entities and structures). All creature entities have default behaviours, sizes, appearances, but attached details can override them partially or entirely.
Details attach to entities and structures entirely at random (Including the number of details that attach, which will often be zero), weighted by region and whatever weights the entity/structure has (e.g. organic things are less likely to have inorganic details, and vice-versa).
Examples of details are stone as a material, stalking-to-repeatedly-spook-then-scaremurder as a behaviour, and suicide notes as a book subject.