Chapter Text
Design Goals
So... What's the problem?
To determine the design goals necessary for this project, first we must define the issues with the existing canon and I will be trying to solve.
1: Sonic the Hedgehog.
The primary hero of the setting, and target of the bulk of story attention, is treated as the generic baseline, with most other characters being able to provide most useful applications of his trademark speed while also having other secondary abilities they can apply to the situation.
This has several knock-on effects. Other characters are sidelined and under-utilised to prevent them from overshadowing the main protagonist, which leads to less varied gameplay and stories, and a constant, ill-defined power creep to try and explain why Sonic remains relevant, as well as various gameplay gimmicks to provide variety in play in the absence of other characters.
2: Eggman.
Practically the only enduring villain of the setting, Eggman’s constant presence as the only member of Sonic’s villain stable is another suppressing force on the series, and even worse, Eggman is a villain who Sonic is actually very poorly equipped to deal with thanks to his massive potential for developing non-standard problems where moving extremely quickly isn’t very helpful.
This leads to plot armour, with Eggman constantly self-handicapping and engaging in foolish behaviours and needlessly limited villainous schemes purely to ensure that Sonic is able to handle them. This leads to plots that are formulaic and less satisfying than they could be, and diminishes Eggman's presence as a villain.
A less obvious problem is that this stifles other characters from getting games and stories. Sonic and Eggman are so constantly fighting that to have a game starring another character at this point would either need to explain why Sonic wasn't involved or to develop a brand new villain since non-Eggman villains tend to die the same game they show up in. Infinite, Kukku, Witchcart, Black Doom, Mephiles...
3: Magic Rocks.
There are no fewer than seven different types of magic rock, many more special macguffins and far, far more infinitely powerful artifacts, and no fewer than three adorable mascot characters - assuming you don't include the entire cast. At this point it’s reached a constant plothole as to why, when confronted with a threat, Sonic doesn’t simply grab a different magic rock to solve the issue.
There's also a big confusion as to what half these macguffins are, how they operate, and why and when they work, quite beyond why they show up in the places they do. This leads to many games and stories completely ignoring or revising even series staples like rings, and people still have no idea for sure how the Chaos Emeralds showed up in Sonic 2 after Sonic 1 even three decades later.
4: Sonic’s terrible friends.
When other characters do show up, their abilities are often inconsistent, their story role non-existent, and more often than not they serve only as nostalgia bait for when these characters were fun and useful, or foils to show off Sonic in a favourable light. Some characters have great obstacles in showing up at all, such as Blaze or Silver, while others simply raise the question of why they’re there and what they’re supposed to be doing, such as Knuckles.
This is also part of the reason that characterisation latches onto and emphasises a single core trait of the character. This makes it easier for them to have "presence" in the story without needing them to actually do anything.
So our goals are as follows:
A: Provide each character their own niche where they can thrive without overshadowing other core characters.
B: Have solid story hooks for them to involve themselves in various stories, with things for them to do when they do get into a story.
C: Provide a stable villain's roster.
D: Consolidate game concepts into a smaller, more focused set that can easily be integrated into stories.
E: Provide a solid core framework that works in 3D, 2D, and non-traditional Sonic game styles, as well as other non-game media. While I can (and do!) go around designing individual Sonic game experiences, this is intended to be franchise-wide, not a specific game.
F: Allow room for story flexibility and growth while providing a stable foundation to hopefully minimise unintentional characterisation and power creep.
G: Remain in-line with original design intent for characters where possible.
Simple… Right?
Well, let’s get started.
Setting Design
Let the Collectathon Begin.
Rings
The natural ambient star energy now common on Mobius after the destruction of the Jewelled Sceptre naturally coalesces into visible concentrations of energy known as rings. Mobians can naturally absorb the energy of these rings, using it as fuel for their special abilities or most complex devices. Most mobians can naturally store 100 rings at once in their own bodies.
While rings are naturally occurring phenomena, technology that uses other forms of energy to store and produce new rings has been prevalent on Mobius for generations, forming such a major part of the world’s economy that most nations use ring-backed currency systems, and rings are accepted as legal tender almost everywhere in the world.
Rings can be found floating in the air as well as trapped within certain objects and are common throughout the world.
Chaos Rings
Unlike normal rings, these rings, also known as colour rings, are formed from ambient Chaos, taking their colour from their respective Chaos Emerald. Each ring coalesces in a random location in an area near its Emerald Haven. A minimum of fifty chaos rings of the appropriate colour is required to venture into a Haven to attempt to recover the Chaos Emerald, with each remaining Chaos Ring beyond that granting more time within the Haven to make the attempt and providing fuel to maintain the Chaos Emerald’s power.
While numerous, Chaos Rings only appear while an Emerald is in its Haven, leaking Chaos into the world, and there is a strict limit in how many chaos rings can be in existence at once, with old, unused chaos rings eventually fading away to be replaced by newer versions somewhere else in the region next time the emerald is in its haven.
Chaos rings are generally found in hard-to-reach places, secret hideaways, and other awkward places. While only a small number can be held for longer than a few minutes, and they cannot be stored electronically, a mobian can safely absorb and expel colour rings as mostly corporeal forms to exchange or store them.
Design Notes: Rings always had a weird interaction with canon, indispensably useful and linked to Chaos Emerald use and simultaneously remaining ignored and omitted or turned into a one-off power-up item, with Sonic holding aloft his trusty power ring before suddenly gottagofasting faster than ever before.
By leaning in this direction, rather than the stakes-destroying “infinitely recyclable key to ignoring all injury” we instead solve another problem - a sense of cost to a mobian’s abilities, or, in other words, resolving “Why isn’t Sonic solving every single problem within the first two minutes by travelling at the speed of light?”. Here, we can have characters do awesome stuff, while attaching a limit to explain why they aren't doing that awesome stuff all the time.
Secondly, with limited lives being out of fashion in game design, this a fresh mechanical reason for players to want to explore levels and get rewarded for mastering routes through the level that maximise their rings, coloured or otherwise. More rings lets players do more cool stuff, which lets them progress faster to offset the time they spent getting more rings.
It also rewards the player for breaking stuff around the map, which, let’s face it, everyone enjoys doing.
Lastly, with colour rings we have both our red ring collectables reward for good play, and in a form that encourages lots of them to be left around to be conveniently snatched away by nefarious types before they can be used to get a Chaos Emerald, and a strict limit to how long that emerald can be used - mainly in story purposes.
The Chaos Emeralds
Fusion: All the Magic Rocks.
Seven mystical stones fundamentally bound to the world of Mobius, the Chaos Emeralds can be found in their Havens, constantly changing extradimensional space connected to Mobius by its emerald, scattered across the world.
A single Chaos Emerald in the hands of a mobian can supercharge their natural star power, allowing them to achieve incredible feats, while machines powered by a Chaos Emerald can harness their incredible energy output to produce unparalleled effects.
Unfortunately this energy comes at a cost. Once an Emerald’s energy is first tapped into, it begins a reaction within the stone, slowly but constantly consuming chaos rings. Should the supply of rings run out, the Emerald will shatter and vanish, reappearing a short time later at its haven, intact once more.
Each Haven for the Chaos Emeralds is a hotly contested location as multiple world powers, mobian and otherwise, seek to gain access to the surrounding chaos rings and the Haven itself. But with chaos rings scattered randomly across the region and the constantly changing Haven potentially requiring many attempts to claim the Emerald, even a claimed haven is no guarantee of swiftly recovering the Emerald once it has been used.
As such, Chaos Emeralds are considered to be tools of mutually assured destruction, too risky to employ offensively and risk being defenceless against another Emerald holder, but vitally important to possess - just in case.
Gathering even one Chaos Emerald is a difficult feat. Should all seven be combined, the resultant force would be sufficient to reshape the world.
The Emerald Guardians
While Emeralds may be used by anyone, each Emerald has an associated Guardian, a mobian instinctively drawn to its Haven and driven, for one reason or another, to protect it from outsiders.
How or why Guardians are chosen is a mystery, but there may be something to the idea that the Emeralds hold a will of their own, subtly influencing the world to advance some unknown agenda.
The Master Emerald
Not a true Chaos Emerald, but an ancient relic from a past civilisation. The Master Emerald holds the ability to stop the chain reaction within an activated emerald, preventing the emerald’s disappearance.
Though this only pauses the consumption of chaos rings, this allows someone with access to the Master Emerald to use their emerald over a far longer period, making the Master Emerald another key target, though its location on the flying Angel Island guarded by Knuckles makes even catching a glimpse of it a difficult feat.
While the Master Emerald has other functions, the only ones who know how to use them, or the cost of doing so, are the Echidna tribe.
False Emeralds
A recent invention, False Emeralds are the creation of Miles Prower, who guards the secret of their creation even more zealously than he does the Yellow Emerald itself. Grey in colour, these artificial constructs share the properties of the Chaos Emeralds, allowing the same massive boost of power in their users or machinery, but with several key differences to the true Emeralds.
First, they require a massive amount of star energy to activate the emerald, consuming fifty rings (on top of any normal ring costs to power the abilities), and secondly they are inherently unstable, lasting only a few minutes after their energy is activated before turning to dust.
While supremely limited compared to the genuine article, having the ability to fend off a Chaos Emerald wielder even temporarily has led to dozens of these being stockpiled by the major world powers, and how many are held within the Central Archipelago is a mystery.
Despite being used more readily in conflicts around the world, their existence has helped to stablise the political environment of Mobius somewhat and provide some protection from the endless aggression of the world’s villains.
Design Notes: Splitting the Chaos Emeralds isn’t very Dragon Ball of me, but combining all the various magic rocks in the series gives them the significance they deserve, while separating them into individually powerful forms allows some important things to happen:
First, it allows much more lopsided opposition between heroes and villains as they compete over an unknown number of rings rather than over Emeralds directly, leading to a less “swingy” story with more opportunities for dramatic confrontation and the opportunity to tie each level or area of a game together in the search for more chaos rings rather than simply snatching emeralds back and forth until someone has seven of them.
Secondly, with each Emerald supercharging what each mobian is good at, this lets other characters get to shine without robbing our protagonist of their chance to show off, and with seven emeralds that’s potentially up to seven characters getting to do cool things, villains included, potentially more with False Emeralds.
Third, this allows for more complex results to stories. Rather than the existing “Sonic cycle”, as IDW coined it, of Eggman coming up with a plan and Sonic thwarting it right back to the status quo, villains can lose the battle but still end up picking up an Emerald, paving the way for larger stakes in the next story as they gather up some chaos rings to use in their next, bigger scheme.
This also allows for more variety of games. Low stakes stories are the perfect place for weaker characters in the roster to get to play in budget titles, setting up high stakes stories for the series’ top dogs like Sonic, while multiple, or even seven emerald stories work for multi-character epics.
And for times when the story needs a power up without getting a full Chaos Emerald involved, false emeralds allow a teaser of these chaos modes as a puzzle element or power up reward without having to commit to anything higher stakes than normal, as well as a nasty, but more manageable, doomsday weapon (False Emeralds make for a perfectly functional warhead, after all).
And what about the various ancient doomsday weapons and horrid monsters? They can still show up just fine, with a Chaos Emerald to power them / release them upon the world, and the biggest nasties that tap into all seven emeralds being the type of unbelievable cosmic threat that makes for good Ten Year Anniversary plotlines.
Mobians
The native inhabitants of Mobius, this genus of small yet robust lifeforms has a wide variety of subspecies with various traits.
While there are many different types of mobian, they fall into a few broader categories:
Hardshell - Armadillo and Hedgehog being the best known varieties, these mobians are defined by having a hard external covering to their head and back. Armadillos tend to be more defensive, with their smooth shell redirecting all but the sturdiest blows, while Hedgehogs tend to be more offensive, using their sharp spines as offensive weapons.
Echidna are distantly related to hardshell varieties, though their spines are soft, long and flexible and they tend to have the more powerful physique more often associated with Short-tails.
Longtail - Dogs, cats, wolves, foxes, jackals and squirrels, along with other similar types like Racoons all fall into the category of longtails, with powerful long prehensile tails some individuals can use as a third hand or a bludgeon - or sometimes both, and tend to have better balance than their shorter tailed cousins.
Short-tail - Bears, Koalas, pigs, apes, rabbits and other, similar mobians. While they lack the defensive properties of Hardshells and the additional limb of Longtails, Shortails tend to be stronger and larger than their cousins.
Despite what one may expect, most Avians are Short-tails, lacking the secondary wings necessary for proper flight, though their feathered arms allow some to glide quite well.
Aerial - A rare, and rather variable type dominated largely by bats and insects, these are defined by the presence of wings in addition to their normal limbs, allowing them to glide or even fly.
Reptillian - A warm weather variant typically found in the equatorial regions, Reptilians still fall into Longtail and Short-tail varieties, with differences between the two being even more pronounced than among their fuzzy relatives.
Regardless of species, all Mobians tend to be exceptionally strong and fast by human standards, and with star energy now abundant, many develop Star Powers, special abilities as variable as the mobians themselves.
This is less rebooting and more codifying things that already seem to be design standards of the various mobian species, giving a basic framework of abilities any new mobian can work from. I will take the moment to answer one potential question however - Why Mobius and Mobians?
Generally speaking, it’s because moving away from the terms in the first place was a design mistake. You want a nice clear term for fans to describe your aliens beyond “anthropomorphic”, which is a very human-centric term, and Mobian persisted in the fandom in spite of Sonic Team’s attempt to distance themselves from the term for exactly that reason. As for “Sonic’s World”, I can think of nothing more symptomatic of the problems that face the series than declaring the entire world literally revolves around one blue hedgehog.
Chao
Fusion: Critters, Wisps, Chao.
Chao are part of the native wildlife of Mobius. Small, morphic lifeforms related to mobians which change their form based on their environment and upbringing. Regardless of form, chao naturally absorb and store Star Energy over time in the form of rings.
Chao forms such as flickies and rickies are most common, taking simple forms to suit their environment and mimic more mundane (and far less cute) local wildlife. Such chao can grant some of their remaining ring reserves to passing mobians when befriended or rescued, such as from Eggman’s badniks.
Meanwhile, Special Chao, exposed to exotic events or mobians during their infancy, develop their own Star Powers, and grant those powers to mobians for a time, allowing them to use it in place of their own Star Power for a time.
Chao are frequently farmed by mobians - not to eat, but to artificially expose young chao to specific mobians or conditions to produce special chao which they drop into combat zones or industrial centres where they can be tapped into on demand.
Design Notes - The already established ability for chao to change their form lets us consolidate them other two mascot characters while having a much closer connection to the series’ lore (and being widely popular, compared to the more divisive wisps).
In effect, when a player encounters a chao they will either receive a quantity of rings as the chao grants them ring energy and then escapes, or in the case of a special chao, that chao will fly along with the player for a time, replacing their aura with a special, zero cost aura supplied by the chao until it leaves. Forcibly deactivating the aura ends the effect prematurely, and the chao leaves immediately.
Since chao are native and universal, they can provide all sorts of gameplay functions, power ups, and puzzle solutions for gameplay with no awkward questions as to why they’re there, or how they’re actually powering all those giant robots.
This also gives Chao Gardens a special use beyond being a cute minigame, with the opportunity for the player to deploy their own chao during gameplay, including special or character chao they manage to breed, which expands a fan favourite into having primary gameplay relevance.
Boosters
An important part of the mobian transportation network, springs and speed ramps instantly propel any who land on them at Sonic Speed. Most mobians at this speed rapidly start to lose speed due to wind resistance, falling down to their maximum speed, but this boost is generally enough to transport mobians who land on them across to the next platform or section of an area.
They aren’t very compatible with humans, who have to worry about things like “G-forces” and “terminal deceleration”, but most areas with mobian populations will use them as an efficient and high speed option to travel across a region.
And this covers the last of our series staples in terms of core mechanics. Boosters now exist for an in-universe reason instead of a lazy game contrivance to avoid having to have momentum-building sections, and can even be justified in massive, road-spanning amounts as we see in Sonic Forces if those places are highways.
Next we’ll take a look at the part you’ve surely all been waiting for - tedious geopolitics.
The World of Mobius
The Place the Stuff Happens
The new composite world, Mobius is inhabited by a mixture of mobians and humans, and is divided into, very roughly, six distinct political regions of importance.
The Blue Emerald
While six of the seven Emeralds have fixed Havens, appearing there time and again since ancient times, the Blue Emerald is special in that its Haven wanders across the world. The Haven can reappear anywhere, and its blue rings spread across a massive area around it. The Blue Emerald brings with it the chaos and upheaval of its namesake wherever it lands.
Its Guardian, Sonic the Hedgehog, stumbles across its new Haven with surprising regularity on his endless travels around the world, frequently thwarting the designs of whichever nefarious villain had found it this time.
The Central Archipelago
A small cluster of islands approximately in the middle of the Emerald Ocean. Most of the islands are small and uninhabited, havens for wild Chao, though a few hundred thousand mobians - mostly Longtails - are scattered across the largest islands.
Despite its low population the Central Archipelago is prosperous, wealthy and far better defended than something of its size has any right to be, with much of its population employed to work in Milestech facilities scattered across the region, producing state of the art electronics along with processed metals, chemicals and plastics.
By far the most valuable export of the region is the False Emerald, produced through painstaking secret methods, with each Milestech facility handling a specific stage of processing the newly formed emerald "seeds" sent out by the main Milestech lab on Cocoa Island. None but Miles himself know the full secret to their creation.
Haven: The Yellow Emerald
If the Blue Emerald has the most variety in its haven, the Yellow has the least, with its yellow rings appearing only within the shores of Cocoa Island, a small island near the middle of the archipelago depopulated during the First Kukku War.
Its Guardian, Miles “Tails” Prower”, faces constant pressure from outsiders trying to lay claim to the archipelago to acquire the most “reliable” of the emeralds. He lives alone on Cocoa, protected by permitting only a few trusted visitors to step foot on its balmy shores, and fewer still to enter the Milestech lab compound that dominates the island.
Angel Island
Almost unpopulated, this floating land mass typically circles the Emerald Sea. The island is almost entirely unpopulated save for two Echidna, guardians of the Master Emerald and curators of the ancient reliquary, a storehouse for archaeological artifacts of long forgotten civilisations to keep them out of the hands of those who would use them for what is, all too frequently, their intended purpose.
Typically a lifelong position, the curators of Angel Island select new members from the small number of Echidna scattered across the world, testing new applicants with the Master Emerald to confirm their suitability for the task. Time, however, has not been kind to the Echidna tribe, with its few surviving members scattered across the world, ignorant of their heritage to the point that most are simply going through the ancient rituals with no understanding of their true purpose.
The Sol Protectorates
Situated to the North East of the Central Archipelago, the Sol Protectorates are composed of smaller tributary islands surrounding the larger protector state of the Kingdom of Soleanna.
Deep in the ocean depths lies the Soleanna Trench, the deepest part of mobius, a vast and almost completely unexplored region, and littered precariously on the sea shelf the Trench are scattered ruins, many of which remain airtight thanks to the ancient technology protecting them. These bubble cities contain a wealth of ancient treasures, forgotten lore, and long abandoned defenders assigned to guard the cities until their ancient masters return.
While Soleanna itself holds a powerful military, its forces are stretched thin protecting the islands of Sol, constantly patrolling the waters to defend against pirates and invaders from nearby hostile states. The King and Queen rarely leave Soleanna's shores, occupied in affairs of government.
The economy of the Protectorates is chiefly tourism, though the nation of Soleanna itself is a major producer of precision machinery and vehicles.
While the population of Soleanna is largely comprised of various Longtail groups, there are a number of Short-tail tribes scattered across the Protectorates, with a wide variety of environments from the temperate Soleanna to the frigid islands of the North Sea.
Haven: The Red Emerald
With a haven on the main island of Soleanna, seat of political and military power in the region, red rings can appear above and below the waves, hidden among the ancient ruins along the sea bed as well as scattered throughout the scattered islands of the Protectorate states.
Its guardian, Princess Blaze Vankedisi, tirelessly patrols the seas in defence of the realm, defending the gaps left by the patrolling military fleets from threats both above and below.
The Mobian Territories
To the southwest of the Central Archipelago, connected to the U.F by a narrow land bridge, the Mobian Territories are actually a vast collection of city states and smaller, largely feudal, clan territories aligned broadly by species. Most varieties of mobian have at least a small showing in the Mobian Territories, jostling for dominance in a constantly shifting set of factions, feuds and outright conflict interrupted only by an outside force having the temerity to interfere in the region.
While technologically below its neighbours, the tense political situation in the region means anyone trying to invade will swiftly find itself surrounded by enemies on multiple fronts, making it a hornet’s nest none of the other world powers much cares to stick its hand into.
Haven: The Purple Emerald lies on Westside Island, one of many small islands situated off the coast of the mainland. A politically neutral territory, Westside is dominated by the Nights Casino, a luxury resort ruled over by Rouge the Bat.
By establishing a system where a single Chaos Ring can buy entry to the Casino’s luxury suites for a chance to win a fortune in rings at the slots, Rouge has managed to turn the entirety of the squabbling clans into her assistants, funneling the purple rings to her without her having to lift a finger.
The United Federation
A large and abundant territory to the Northwest of the Central Archipelago, dominated by a strange, excessively tall alien species known as “humans”, who have inhabited the region since arriving from an unknown alien world untold centuries ago, filling a gap caused by the near extinction level event caused by the area’s Echidna population just prior to their arrival. While at a disadvantage against the local wildlife, humanity’s strongly cooperative nature and advanced technology has helped them carve themselves a stable niche on mobius.
Though humanity has at this point displaced the original mobian population of the region, many reptile and insect species still persist in the more southerly parts of the territory, along with a more metropolitan mix of other species who have settled in the human cities, though this rarely happens in reverse. Mobians might be too short to live comfortably in human settlements, but humans tend to be too fragile to survive in mobian settlements, which routinely involve contraptions to simply catapult them to their destinations at top speed.
Humanity has had a significant cultural impact on mobian cultures, with clothing, textiles and protective equipment - all literally alien concepts to mobians - being major exports, along with food and entertainment media, and human languages have spread to being a universal lingua franca across the globe, contributing to the phenomenon of mobians categorising themselves after the alien wildlife that humanity brought with it to the planet like hedgehogs and cats.
While humans are unable to directly use Chaos Emeralds or rings, their high level of technology has harnessed both of these for their machinery, fuelling an impressive defensive war machine.
While not aggressively expansionist like the Kukku Empire, the military arm of the United Federation, G.U.N constantly seeks to destabilise its neighbours through a combination of espionage and false flag operations in order to maintain its political superiority, and cooperates with a number of criminal organisations and engages in a number of nefarious secret projects scientific and otherwise due to a lack of oversight from its democratically elected civilian authority.
Haven: The White Emerald lies within Station Square, a coastal region on the west coast of the United Federation. Due to its presence a number of clandestine G.U.N bases can be found in and around the city, with multiple projects ready to make use of the emerald’s power should the opportunity and need arise.
Its current guardian is Silver, an artificially bred hedgehog mobian who has served G.U.N since birth.
Babylonia
Situated on the vast Eastern Continent, the lands of Babylon extend across a vast and varied landscape of thick forests, soaring mountains and huge inland lakes. Populated primarily by Avian mobians, Babylonia has been a stable political entity since ancient times, when the three kingdoms of Hawk, Owl and Albatross finally collapsed into a single ruling authority, the Kukku Empire.
While traditionally the Kukku were disinterested in expanding their already extensive territories, this changed with the rise of the Great Imperator, who converted much of the Kukku’s predominately agricultural industry into building one of the largest war machines the world has ever seen.
The Kukku then invaded Cocoa Island, seeking out its Chaos Emerald to fuel their worldwide expansion, wiping out the population save for one single mobian - Miles Prower. This turned out to be their greatest mistake, as the young Miles proceeded to engage in a surprisingly brutal guerilla campaign against the occupying forces, converting destroyed materiel into an ever more complex array of combat mecha, weapons and gadgets until the invasion force was not only crippled but killed several key members of the Kukku hierarchy, including the Imperator himself, who attempted to stabilise the collapsing offensive by employing the power of the Green Emerald, and the destruction of their floating fortress Sky Babylon with all hands lost.
It has taken seven years for them to recover their lost emerald and stabilise the upheaval in their home territories after the First Kukku War, and they are now itching for a second, raiding rival territories as they prepare for their next grand offensive.
Haven: The Green Emerald
The Green Emerald’s haven is at the heart of Ancient Babylon, within the Imperial Palace. It is jealously guarded by its guardian, Emperor Jet. Due to the massive area the green rings can appear over, each time the Kukku employ the Green Emerald sparks a long and painful period struggling to recover it. A major aspect of their desire to invade other territories is in order to gain a second, more convenient, Emerald.
The Metropolis
Situated to the south of the Central Archipelago, the Metropolis is an enormous technological city many times larger than the islands it was originally built over. Ruled over by the Eggman, Ivo Robotnik, a once-human scientist now a mix of man and machine, the Metropolis is a combination of a desperate underclass of humans, cybernetically enslaved mobian workers, and various criminal elements seeking sanctuary from more civilised nations.
Cyborg slaves work its innumerable foundries to build the endless robot armies of their dread master, constantly raiding the surrounding regions of the world for resources and fresh slaves to expand the shores of the mechanical city ever further, while the most amoral scientists carry out dark experiments deep within the smoky bowels of the city.
Haven: The Black Emerald’s haven, previously known as South Island, is now buried beneath a mile of steel known as the Iron Fortress, with robotic seekers roaming its smog-darkened streets in constant search for the black rings.
Shadow the Hedgehog is its guardian, but has left the area, defecting to the U.F and leaving it undefended. As such the Black Emerald is the most frequently used emerald, constantly being employed either in the Eggman’s experiments or to power his Death Egg satellites to rain destruction down on his enemies.
While this doesn’t cover every part of Mobius, by design, it does set up our major players in the setting, with a nice spectrum of morality and plenty of scope for our villainous groups to get up to mischief. With this in place we have plenty of different environments for Sonic to run around in, humans and mobians both without any two-worlds nonsense, and even some basic trading - not that we need to worry much about that sort of thing in our average Sonic game as anything more than window dressing.
So with Goal D more or less done, next up we need to start fleshing out our characters, starting of course, with Sonic himself.