(This information probably ought to be better organized at some point.)

"Following the disappearance of the Alicorn Brand, the players take on the role of "The Embers" the team of Brand's former retinue protecting the northern kingdom in his absence from various episodic threats. (MHP setting)

This is an early and those lower magic MLP setting, think something similar to Conan the Barbarian."

"Ah, it sounds like the defeat of Discord is fairly recent, within a mortal pony lifetime."

"yes, it's been only a few decades at this point"

character creation:

"Character Creation:
The Embers are not wet behind the ears and each is indeed a legend in their own right. Gathered under Brand's banner during the alicorn's own extensive adventures, they come from just about any region or peoples under the sun.

Aside from general description, characters should have the following:
*Heroic Quality: The dominant attribute that defines them as a heroic figure, courage, prowess in battle, wisdom, magical study, cunning, agility, etc. This should be the way the majority of ponies would describe them in a positive sense.

*Strengths: The three things the Ember most excels at aside from the heroic quality. Example: A mighty warrior might have the heroic quality of Battle Prowess coupled with the Strengths of: Physical Might, Expertise with the Blade, and Incredible Resilience.

*Weakness: At least one thing that is a known or obvious failing or vulnerability to the character. 
Example: Brand has a notorious temper that caused him severe troubles in his youth. It remains a part of who he is even if he's no longer governed by it.

*Deed & Legend: The Embers were gathered in heroic epics and adventures. Each should have at least one major event that created a large part of their reputation (Deed) and the events that led to them and Brand meeting and their being recruited (Legend). These can also be the same event.

Each character has the tools of their trade as well as "The Lord's Brand" a magical mark of their rank and position. Aside from acting as a symbol of authority in Brand's lands, once per adventure a character can call on their magic for one of 3 effects.
Starfire: The pony produces a single large flare light that can be launched up into the air as a signal. These are always visibly distinctive to the character, allowing teammates to recognize who sent out the signal.
Hearthfire: Brand's single biggest claim to the frozen lands is his ability to use his copious fire magic to repel the cold of the land. The embers can tap into some of this gift at will to surround themselves in a warm glow of energy that protects them from the cold.
Battlefire: Lastly the Embers can call Brands devestating flames into their weapons or magic to enhance them for a short while."

"However, a couple clarifying questions on The Lord's Brand's powers, please:
1: Is that one effect per adventure, or each of the three effects once per adventure?
2: Around how long does Hearthfire last?"

"One of the powers per session and hearthfire lasts long enough. That is, unless the session ends up with a significant time skip in the middle of it, it will last the whole thing."

"Thanks.  Though is hearthfire an area of effect centered on the user, then, so that one member of a team can use it to protect the whole team (and non-Embers accompanying them) while others are still ready to use starfire or battlefire?"

"It's an aura that generally doesn't extend past a meter, with the effect dropping off with distance. There's some room for flexing, magic is still young and wild at this time, but the further it's pushed the less time it will last.

Though a pony skilled or trained in fire magic could probably augment that a bit by using their own power."

"So all of the species from the show would be present, including Gryphons, zebras, diamond dogs, hippogriffs/seaponies, kirin, buffalo and dragons.

There's also Harpies and Aranea, who are original to this setting.

Gryphons are currently largely split into roving war-bands under militant generals.

Zebras along with Saddle Arabian ponies have a pretty developed culture and civilization across the sea in the Farlands.

Diamond Dogs are rarely, but not never, encountered above ground owing to their communities largely being subterranean in nature.

Seaponies/Hippogriffs have have yet to flee to the sea, but they do have access to transformative magic. 

Kirin are still largely isolated and have yet to take on their magical silence.

Buffalo are largely unchanged from the show.

Dragons are currently ruled over by the 2nd Dragon Lord, Ossiberus. There are rumors he's planning to direct the dragons in some kind of hostile action as he has recently been calling many of them to the center of his domain.

Harpies come in least, standard, and greatest varieties. Their head and body largely resemble ponies but with the wings and hindlegs of birds. 

Least harpies are half the size of the regular pony and are vegetarian. They largely live in tropical climates in family groups and have an aptitude for music based magic.

Regular harpies are pony sized and with a harsh and militaristic manner. They frequently live in mountain fortresses.  

Greatest harpies are not available and are built on the same scale as adult dragons.

Aranea are spider ponies. They have access to poison, limited shapechanging magic, and mental magics."

""Their head and body largely resemble ponies but with the wings and hindlegs of birds."
Bird wings replacing forelegs, I'm guessing?"

"yes"

"@Maddie:
Is this world known to have or not have an underdark equivalent?  If it's known to have one, what's known about it?"

"It has a number of underground kingdoms so I'd say close enough. But at this point they'd be pretty rare knowledge and your average pony would likely consider them the stuff of legend.

Not that this would mean you couldn't be a Diamond Dog treasure hunter, but it does mean you could expect ponies to need time to get used to you."

batponies:

In ancient times, before the coming of the windigos, the four tribes of ponies shared their ancestral homeland.  As the earth ponies farmed the land to provide the bulk of ponykind's food, the unicorns worked magic from the crafting of artifacts of domestic convenience to the movement of the very heavens, and the pegasi shaped the weather and mustered heroes and legions to defend the land, the nocturnal batponies watched in the night for those threats that might evade the pegasi and delved into the earth for those minerals desired by the ponies but not yet within the earth ponies' ability to grow.  Sometimes the roles of the fourth tribe would overlap, for now and then diamond dogs would make opportunistic raids of the surface, safe in their tunnels from the militias of the earth ponies, the warriors of Pegasopolis, and all but the most powerful or specialized Unicornian mage-knights.

That they were yet distrusted by the other tribes goes without saying, for in those days no tribe trusted any of the others.  While the other three were interdependent, however, and would remain so as they fled south to escape the hungry ice, the batponies in their delvings had discovered the vast and winding caverns deep beneath the world's surface, untouched by Sun or Moon, isolated from weather above, and saturated with chthonic magics that nurtured life in that abyss where only the dim glows of magical minerals, molten rock, and life itself, whether naturally or from its tools, pierced the elder darkness.

Rather than join the competition for warm and distant surface lands, it was _down_ the batponies migrated, deeper than even the cold of the windigos could reach.  There they lived, in villages amongst the close, humid, luminescent black jungles of the deep or in strange-lit cavern-cities of monumental stone where schools studied magics of unending night and warrior orders trained to wield jeweled blades of magma-forged shadowsteel against both proud and greedy diamond dogs and the Things that dwelt in the yet-deeper shadows or the fire of the earth.  Generations passed, the surface to the ponies of the deep increasingly distant history while those above forgot the fourth tribe almost entirely.

But still they were ponies, and so it was that there came a night when Princess Luna of Equestria in her dreamwalking made contact.  From this, for the first time in a great many years, did batponies again fly under open skies -- and yet, not only had they no home on the surface, welcome as they were told they would be in Equestria, they found that their adaption to the depths was not so easily cast off.  In the old days, Sun had been quite tolerable to them, and they could individually shift to a diurnal lifestyle with as little or much difficulty as a member of another tribe could become nocturnal; now, it was an actively painful hindrance to any batpony lacking sufficiently umbrathurgy ability to protect themself.  Additionally, much of the equipment they'd learned to craft that served them well in the depths failed in the surface day, or sometimes outright failed even in surface night.

Thus, although contact had been reestablished and some trade links were made, there would be no great flow of batponies to the surface -- indeed, most surface ponies might live their whole lives without realizing batponies existed.  The only significant group movement of batponies to the surface was the establishment of an elite section of the Night Guard answering to Princess Luna and supplied mostly with Equestrian equipment; barring a few accidents (because ponies are still ponies even when some of them are leathery-winged and far from home), batponies continue to be born and raised only in the depths, and only a minority of the Night Guard's batponies have chosen to remain on the surface after retirement from active duty.  As Princess Luna has taking a liking to their aesthetic, however, many Night Guard pegasi have illusion magic included in their armor to create the appearance of batponies while they're on duty -- which has had the side effect of further reducing the average pony on the street's knowledge of batpony existence, since even some residents of the capital might "know" that the spooky-bat-dragon-pony-thing look comes off at the end of the shift.

first mission:

""Our tale begins the 7th year since the founding of Hearthhome, capital of the northern lands and fortress of Lord Brand, in this home of heroes grand. That winter, when the storms rose high and the snows froze the land, our Lord Brand, as was his want, departed on a journey to the southern lands, to converse with the Alicorn Princesses there on matters of import. In his absence, as he often has, the management of the lands he has tamed is given over to his friend and confidant Chamberlain Frostway. But though the chamberlain handles the simple matters of the day, protection of the lands falls to Brand's Embers, the mightiest of the northern heroes, each pony a legend in their own right, and in their hooves these treacherous and frozen lands are secure.

The lands are secure but not safe, for the winter is ever ready to claim any pony unwise enough to walk before her as she freezes the land before her. This eve a mighty storm blankets the land, and though none knows what flight of foolish youthful fancy took hold of the mind of Little Spark, Hearthtender and pupil to the mighty Brand, that it should cause him to stray into this frozen night, but take hold it did and his absence went unnoticed until well into the evening meal.

When his absence was realized, great was the uproar, for though Little Spark was held dear to the heart of the Lord of Flame, he was not lacking for the admiration and love of all in Hearthhome. More precious than the greatest of jewel in the mighty treasure hall beneath this very fortress, upon realizing he might be lost to the storm besetting the land, all were rallied to begin the search.

Though many hooves be willing, it is only those brave Embers who can truly risk pursuing him into the wild night. As all of Hearthhome searches within the stones of the capital, it falls to these heroes to find the little colt, that he might be returned to those to whom he is most precious." 

TLDR: You are members of Brand's Embers, the mightiest heroes in the lands north of Equestria so recently claimed by the Alicorn Brand. Whilst the master of these lands is absent his young ward has vanished into a blizzard ravaged night and it is up to the players to find and save him."

first mission pregens:

"Name: Smokey Quartz (Pegasus)
Heroic Quality: Vanishes like ghost
Strengths: Agility, Quick and smooth tongue, Trap Spotting
Weakness: Slender build and Greed
Deeds/Legend: Far off in the kingdoms of Saddle Arabia there arose a legend about a "Princess of Thieves," a brilliant mare who infiltrated even the most cunningly of sealed treasure room before stealing away the most valued of prizes. Her identity was unknown to all and none put together the lovely visiting noble who always arrived to the courts just weeks before the theft. At least not until the "Iron Heart of Telmaz," the magical device that powered the guardian statue and all the traps in the Caliph Silkflow's treasure chambers, was stolen from out of the statue itself and without so much as a coin missing from the now defenseless horde. While no blame was placed upon the visiting, and now missing, noble Simple Glow, a visiting foreign Alicorn was found near that section of the palace and accused of the theft. Burdened with finding the thief to prove his innocence, Brand tracked Smokey Quartz across the desert for 40 days and nights. Though once she was found she proved unable to escape from Brand's power, the Alicorn was forced to admit he admired her skills and would hardly wish to see such a talented pony rot in a prison. So Brand returned the Iron Heart along with a story of having slain the thief in battle, the story being backed by Simple Glow, who had been cruelly taken hostage by the dead thief, the court accepted the return and the two departed, with Smokey Quartz shedding her disguise to joining Brand in his retinue both out of gratitude and out of a desire to see what adventure it might bring.

Name: Battered Blade (Earthpony)
Heroic Quality: Unending Resilience
Strengths: Master of the Waraxe, Mighty, Master of Thrown Axe
Weakness: Not too sharp
Deeds/Legend: Blade was born in the lands of the two princesses to the south and is even a distant relation. However he is very distant and even in his own family's line he is nowhere of importance. As a result he had accepted for himself that he never rise in station and that the most he could ever offer his house and country was the might of his weapons in battle. This changed for him when he returned from a visit to the capital to find his family estates in flames and his family dead. Learning of a fiery Alicorn who had been visiting and was the sole survivor, he leapt to accusation first and the two met in an immense battle. In the fight their hearts reached out to each other and Blade was made to see that the noble warrior before him would not have committed such a heinous deed. Having reached this conclusion he listened to the Alicorn and his version of the events. Having listened, he then joined Brand, to both seek out the dragon who had destroyed his family and then to journey on with the pony who had given him a chance to move forward from such a horrible time in his life.

Name: Flow Break (Pegasus)
Heroic Quality: Impeccable navigator
Strengths: Great swimmer, Great Flier, Sharp Eyes
Weakness: Incredibly Clumsy on land
Deeds/Legend: When Brand was first traveling the frozen north he visited the port town and fortress of Icewatch. While he was there a brutal storm swept in and began to batter at the bay outside of the town. In the flashes of lightning those in the fortress could see the great ship, The Flowing Flame, beginning to sink out in the bay. Brand had come to Icewatch to await that ship which was bringing his retainers across the sea. Brand put his demand to Lord Coldwing for a boat to go out to brave the storm to rescue the lives aboard the ship. While neither the lord nor any of his court had the bravery to risk themselves upon the water, Brand found his aid in a simple fisherpony who was, like many of the town, sheltering in the fortress from the storm. Flow Break, with his legendary mastery of the sea and winds piloted his own ship out into the teeth of the storm and between the two of them they were able to rescue all lives from the sinking ship. Realizing that he would bear the consequences of having shown up Lord Coldwing and his court for as long as he remained in Icewatch, Flow Break decided to leave with Brand and his retinue when the storm finally abated.
  
Name: Wither Pie (Earthpony)
Heroic Quality: Gloomy Seer
Strengths: Mighty, Brilliant Geologist, Skilled Fortune Teller
Weakness: Constant miserable mood 
Deeds/Legend: Wither was well onto making a miserable name for herself early in her life. As far back as she knew she was frequently plagued by mysterious visions of the future, especially of imminent disasters. To her great upset she was never able to prevent any of them and she was barely an adult when she began traveling about the land. However the fact that wherever she went she predicted disasters that soon befell the ponies around her caused her to become known as a harbinger of the same disasters. She was forced to travel not only fleeing her own visions but also to flee angry mobs seeking to destroy her. This continued on for years before she found herself in a small town below a frozen mountain. Besieged by a vision of the town buried in an avalanche she tried to warn the ponies but was ignored save for a visiting Alicorn and his retinue. Catching up with Wither shortly after she fled the town and surprising her as one of the few times her warnings were taken seriously, she told them all that she knew and that if the town could not be evacuated it would be destroyed. It was then that she was given an even greater wonder, as the Alicorns fiery magic was able to stop the avalanche and became the first time anyone had been able to prevent one of her visions of tragedy from coming to pass. As the first pony to believe her and the first to be able to actually make use of her visions Wither Pie immediately swore loyalty to Brand. 

Name: Star Call
Heroic Quality: Master Musician 
Strengths: Master of all instruments, Amazing Scholar, Brilliant illusionist
Weakness: Neither strong nor fast, controlled by his curiousity
Deeds/Legend: Star Call has insisted that he has no legend of his own and others have insisted this is because he has spent so much time alongside Brand. Originally Star Call was the legendary bard who first crafted the songs regarding the defeat of Discord by the Twin Princesses. He served in their court for long enough to become familiar and to train many apprentices. But when Brand, fresh into his journeys, paid a visit to the court of the two princesses, the bard could see in the Alicorn the same beginnings of a legend he'd once seen in Luna and Celestia. Never able to restrain his curiosity, Star Call immediately abandoned his position to follow after Brand, a feature Brand considered more a nuisance than an asset until years later when Star Call's hypnotizing melody saved Brand from a giant stone serpent. 

Name: Little Bite (Unicorn)
Heroic Quality: Commands the Loyalty of Animals
Strengths: Great Survivalist, Scrappy Fighter, Surprisingly Sturdy
Weakness: Bad at speaking, Uncivilized, Uncultured
Deeds/Legend: Little Bite originally was known in legend as "The Black Beast of Boran," as ponies dwelling near that forest had many legends of the strange snarling creature that would strike out on lone travelers. The attacks had spread out and become more frequent, with many wild and varying descriptions until they eventually put out a request for a pony to help save them. It was the alicorn Brand that answered this call and venturing into the forest learned the truth. The truth was that many years ago a unicorn foal had been lost in the forest, growing up alone with the wild beasts, the feral pony had mastered an affinity to animals but had become unable to recognize ponies as his people and had attacked them both for food and to defend his territory. When Brand brought the unicorn in, he was disgusted to learn that the townsponies intended to kill the unicorn for his crimes. Brand interceded and insisted that he would take the unicorn away instead (though convincing them required more than a sleight threat). Though it took years, Little Bite has learned some basic language and even been convinced to wear the occasional clothes, but he remains an intensely wild presence among the Embers."

"Star Call is a unicorn"