Well author gave the thumbs up/like in the discussion thread so time to move the final product over.
Planet Hawktor II of the Hawktor system
Hawktor II was and still is a prime example of abnormal worlds and how a place can be far different than what it appears to be at first glance. While from orbit to the Taurians, it appeared to be a 'typical' earth-like world, upon analysis of the local flora and fauna turned up a rather stark difference to the norm. Namely that the planet and the ecosystem that had developed on it had concentrations of metals, heavy, rare-earth and otherwise in such quantities that the scanners had to be re-calibrated so as to give comprehensible results. While this made everything on the planet lethal and/or highly toxic in regards to consumption forcing the settlers to rely on in-door farms, extensive water-filtration systems and hydroponics; it was an incredible boon of easily accessible mineral wealth. This was due to the native organisms expressing the metals absorbed in teeth, hide, hair, scales, claws, bones, bark and so on. Thus the colonists did not need to mine for minerals but instead could chop down the local tree equivalents or 'shear' (often requiring diamond-tipped rotary saws) various wildlife.
Unfortunately this rich source of valuable metals made it a prime target during the Reunification War with a disproportionate number of SLDF forces blitzing the system. While like all Concordat settlements, Hawktor II had defense craft and orbital defenses, it's small population prevented them from having much in the way of a proper PDF and thus fell relatively quickly. Oddly enough, the SLDF command staff in charge of this thrust of the campaign received multiple 'philanthropic donations' from several League companies associated with resource extraction and metal processing. Also that said same companies were granted exclusive mining rights to the planet after the SLDF forces had finished 'liberating' it.
After establishing themselves (and tearing apart the existing food and water infrastructure for obviously superior* SL replacements) said companies went about striping this mother-load dry in the name of buckets of money the Star League. To their horror, it was found very little profit was to be had (since the Taurians were not offering their expertise or knowledge on how to aquire the resources). Prime examples were that the normal lumber-jacking equipment imported was completely useless against the local foliage and resident equivalent of the Bovidae family tended to have metallic hides strong enough to laugh off projectiles that weren't in the 'anti-tank' category and up. Shackled to this money-consuming white elephant, the companies tried to keep afloat in face of various loans that they had taken out for this venture; while slowly but surely distancing themselves from Hawktor II however possible. By the time of the Amaris Coup, the world had been all but abandoned by corporate interests with only an SLDF garrison on station to 'wave the flag'. However said occupation had taken it's toll with the planetary population shrinking by a third over time (due to expense of importing sufficient food and frequent delays in water treatment facility replacement parts) with the industrial and technological capability of the colony decreasing similarly as the Star League had no interest in ever letting the Taurians re-arm in any meaningful way.
All the analysts (from the companies that sold said food and water infrastructure in the SL of course) had 'studies' that their methods would be far better and more efficient than anything the Periphery could ever make.
Even after SLDF forces withdrew; first for Kerensky's invasion of Sol and then later for his exodus, Hawktor was a shadow of it's former self. With only a handful of cities holding on via previously hidden pieces of the original food and water infrastructure (the League equivalents having broken long ago with no replacements ever being sent) the planet could barely support one million people. Worse the greater Concordat was unable to assist due to it frantically attempting to rebuild what it could in preparation for the next would-be invader to take a shot and with data tampering by their former overlords, had actually lost knowledge and/or the locations of multiple colony worlds. So in the end, Hawktor II was left to fend for itself as best it could; alone in the dark and forgotten by their former kinsmen.
The seven cities that remain are situated on a massive north-south running mountain range (called the 'Spine of the World') that splits the largest continent on the planet in two. The reason these particular settlements survived Star League and the aftermath of it's fall are intertwined. First, due to them being considered 'unimportant' due to their locations the Star League enforcers never bothered to properly remove and disassemble all the original food, water and industrial infrastructure meaning that the cities could feed themselves (and maintain their equipment) even after supplies of the 'proper' League equipment stopped coming. And after the Fall as various new and old pirate groups began looking for easy pickings the mountains were far too rough to safely land even spheroid dropships and the locals had long since destroyed the original landing pads for the cities. This forced any pirates looking for plunder to land a good distance away and then force their way through many kilometers of untamed wilderness. And if one does not have a local guide from the cities showing how to safely traverse the regions, travel becomes very dangerous, very quickly.
To the west there are the 'Irondale Fens' a swirling mishmash of marsh, swamps, lakes and dense old growth forests fed by the near-constant mist, fog and rain formed by heavy clouds forming over the ocean being blown into the Spine. While there are land routes through the region, they are few and far between resulting in mechs more often than not being forced to wade through 'knee' (or waist depending on height) muck and water. This is a danger since most metal alloys and even standard armor used in the Inner Sphere give similar sensory impressions to the native wildlife similar to dead or dying organisms. As such mechs in the water are nearly constantly attacked by rockleachs, widespread scavengers that burrow through the metallic hides of animals to lay their eggs in the flesh within. While electrical wires and energized myomer will kill the animals when bit, this damages the internal systems of mechs leaving them limping or in extreme cases unable to move. Worse yet, the smell of dead rockleachs quickly attracts larger predators which more often than not become hostile for any number of reasons.
While highly dangerous to the unprepared/informed travelers, the Fens have the advantage of ready supplies of fresh water, even if due to the high-metal content dust present everywhere it needs to be purified in order to be safe (rain collection and mist catchers are in fact the primariy source of water for the cities). This is not true for the region in the rain-shadow of the Spine, the Howling Wastes. A vast expanse of sun-blasted rock, sand and sparse hints of greenery here and there, the few oasis's are hopelessly hyper-saline and metal rich, conventional purification systems will choke and fail attempting to process it. Only the organisms specially adapted to this region can safely gain the water they need from such sources. A second difficulty is due to the interaction between the statically charged dust-storms roaming the region and the high metal content in the sands and rocks; there is a near-constant electromagnetic 'haze' resulting in conventional sensor and communication systems becoming scrambled or not working at all. This can often result in forign invaders/expeditions becoming hopelessly lost. And if they stumble onto an oasis, they find out that not only are the waters highly toxic to humans, but there are predators lying in wait for potential meals to come and have a drink. Predators that often decide that these soft-shelled pink things look very edible.
While the fauna and flora of the planet can take heavy tolls on the personnel and machinery of invaders, it is not a perfect defense. And even though the inhabitants can no longer produce modern weaponry or combat vehicles, they are far from defenseless. Should an assaulting force make their way to the mountains, they are forced to take the few routes capable of supporting mechs and heavy vehicles which can be rigged to collapse at a moments notice. All the while dumb-fire missiles, artillery and what the Inner Sphere would classify as 'superheavy rifles' rain down on them from what appears to be form every angle. However unlike many factions in the Inner Sphere and Periphery, Hawktor does not salvage as much as possible of any downed battlemechs and vehicles. This is due to the industry and knowledge of how to maintain and make spare parts for a great many aspects of said machines being lost over the centuries...with one exception. Due to a stroke of luck (and pirate carelessness) during one raid the cities managed to capture a technical manual for mech fusion engines along with the tools and some spare parts for them. Ever since then local forces have made a point to try and extract any and all fusion engines from downed pirate mechs to slowly but steadily improve domestic electrical production. Since while they have managed to bootstrap their way to maintaining the machines indefinitely, for the foreseeable future they will not be able to make new ones.