The Miracose Order here was originally designed for the same setting that I made that magic system for. Unlike that magic system, the Miracose Order as an organization could be dropped into just about any setting with only minor alterations. They’re a vicious, power-mongering order of spies, assassins, and sorcerers steeped in shadow magic who can serve as anything from the villain of a minor side quest to the main antagonists of an entire campaign. They have sort of a vaguely Red Wizards of Thay-esque vibe to them.
The Miracose Order is often lumped in with the other two religious orders of the Empire, but its members are actually quite dedicated to worshiping nothing but darkness as an abstract concept. The notion of worshiping specific beings is repulsive to them, as each lives in pursuit of only their own exaltation. This is so much the case that it is common amongst them to kill or sabotage one another in order to advance in the Order, and they are even more prone than other organs of Imperial government to fighting with other Imperials, not to mention themselves.
The Miracose Order is extremely unstable and you cannot count on anyone for loyalty. As such, Miracose agents depend on no one but themselves in the long term and have a culture of extreme self-improvement, monstrous cruelty for the disobedient, and calculated rewards for obedience. There is no loyalty, only fear of the consequences of rebellion and greed for the prizes for success, so the Miracose are extremely concerned with being personally capable enough to deter or prevent rebellion, further deter rebellion by being as publicly brutal as possible to traitors (including anyone whose failures grow to the point where they are either intentionally sabotaging their master or else are simply incompetent enough that they’re worth more as an example anyway), and insuring that rewards are just big enough to keep minions interested in receiving them without giving them enough power to pose a threat.
The Miracose Order is headed by the King With Three Shadows, sometimes also known as the Shadow King. His three lieutenants hold the rank of king’s shadow, each one leading one of the three shadow cults. These three cults are first the Cult of the Eye, inquisitors who specialize in disguise, stealth, and manipulation both pleasant and torturous, whose mandate is to find all hidden information. Second, the Cult of the Reaper, assassins and warriors who specialize in ambush, terror, and sheer indomitability in melee combat, whose mandate is to destroy the enemies of the Order. Third, the Cult of Eternity, scholars and occultists whose expertise of dark magics is unmatched in the Empire, whose mandate is to acquire new and forbidden knowledge for the Order. Rumor is that the Cult of Eternity’s primary goal is to uncover the secret of immortality. Some claim they already have.
Because the King With Three Shadows holds a seat on the Imperial Senate, the Miracose Order in general finds it to their benefit to preserve the Empire, all else being the same, and the Cults of the Eye and Reaper are frequently used as spies, assassins, and agents of terror against enemies of the Senate (and before them, the emperor). Officially, the Miracose Order only has authority to kill when on a mission for the Empire, but it is an open secret that they exceed the limits of their legal authority whenever they think they can get away with it.
Each of the three Miracose cults has their own structure beneath the king’s shadow who runs it. The Cult of the Eye has very loose structure. Individual inquisitors of the cult are assigned broad tasks, such as to know everything that goes on in a certain province, or to gather up blackmail on as many members of a certain organization as possible. The inquisitors are then given leave to accomplish their objective however they see fit. Typically they will make contacts and informants, appointing their most trusted and proven servants as lieutenants, who themselves act as sub-inquisitors assigned to specific tasks, such as to investigate specific individuals in the target organization or specific counties of a target province. When an inquisitor dies, they are succeeded by their own chosen successor. If they do not pick out a successor in advance, the lieutenants fight for the position. The exact hierarchy beneath the lieutenants varies between inquisitors, from the very simple system of each lieutenant having minions who can eventually become lieutenants to organizations as byzantine as the Celestial Order. Being that inquisitors need to remain secret to do their job effectively, most of them favor simple, easily concealed (though compartmentalized) systems.
The Cult of the Reaper has a more rigid structure. The Shadow of the Reaper commands the Miracose lords, the most publicly known members of the Order. Each lord commands several dozen reapers, trained in the harsh and sometimes lethal Reapers’ Academy. The primary schools of the Academy are the Cloak, Wings, and Scythe. Cloak reapers are lone agents, skilled in swordplay, sniping, and stealth, wing reapers are powerful scriers and move swiftly through shadow magic to find and eliminate targets from great distances in very short amounts of time, and scythe reapers are the most direct, commanding small private armies and smuggling them into fortified cities and castles before cleaning them out from within, killing their target and anyone who gets in their way. Reapers also scout for potential students for the Academy, sometimes kidnapping them to take them there against their will.
The Cult of Eternity retrieves and studies forbidden magic. Much of the magic they recover is then disseminated through the academy to the other cults. Some secrets, however, they keep for themselves. Individual occultists frequently keep secrets as well, and the entire cult has a huge culture of secret-keeping and secret-stealing. Knowledge is the currency of the Cult of Eternity. The occultists of the Cult of Eternity often assemble minions to aid them in their expeditions for forbidden lore, whether a small team or an army a hundred strong. While all occultists can theoretically work independently, it is very common for a recent graduate of the Academy to seek apprenticeship under a more experienced occultist, hoping to absorb their forbidden lore in exchange for acting as a competent and initiated lieutenant.
The Miracose Order is famous for using shadow magic and swordsmanship together. While the reapers are most adept, sword and shadow training are staples of all reaper cults. Using umbra to increase reflexes, reaction time, speed, and for bursts of incredible power, Miracose agents are terrifying foes in melee combat. Additionally, they can create all manner of shades, having refined shade creation into an art. While many black mages can infuse umbra into a victim willing or otherwise to create a shadowed version of themselves, the Miracose can reshape them entirely, creating bulky shadow vanguards, massive shadow beasts of war, winged aerial troopers, all created from perfectly ordinary peasants and copious amounts of pure terror.
Due to their heavy dependence on shadow magic, the Miracose are also experts in terror tactics. Umbra causes fear and fear causes umbra, a vicious cycle that the Miracose are all too happy to encourage. Miracose torture and terrorism provide the raw materials for their shade armies, and much of their fearsome reputation comes from their horrific harvests of bodies and fear, often against the peasantry of the empire they’re nominally defending.