The Lady of Mysteries is a god of tremendous power, even among other deities. Her dominion is the Weave, the sum total of magic, from which spells are drawn. Like magic itself, Mystra has undergone many changes over the millennia, including two known passings of her mantle.
The faith of Mystra is pervasive throughout Faerûn, which is unsurprising in a land so touched by magic. Her worshipers include those who use magic or work closely with it, such as alchemists and sages. The goals of her faithful are simple: to preserve and promulgate magic throughout the Realms. Mystra's faithful watch for those who demonstrate magical potential, and they help such people find tutelage with a suitable mentor. She communicates through her Chosen, by sending a Beast Lord or pixie, or through animals that are blue, white, or multicolored.
The blue-clad priests of Mystran temples, called dweomerkeepers, wield both arcane and divine magic. Mystra inspires magic-centric organizations such as the Knights of the Mystic Fire, her foremost martial champions. In cities and towns, the Children of the Starry Quill serves as an information and spy network, while the Order of the Shooting Star pursues her interests in the wilderness. The secretive Sisterhood of the Silver Fire opposes the Cult of the Dragon, tracking down and destroying copies of the Tome of the Dragon, the book that details how to turn a dragon into a dracolich.
Mystra relies on Chosen more than most deities, and the ranks of her Chosen include the Seven Sisters (the daughters of Mystra, including Alustriel Silverhand, Laeral Silverhand, and the Simbul), Elminster Aumar, and other legendary spellcasters. She gives her Chosen the ability to call on silver fire, a destructive manifestation of pure magic that can also restore magic to places that have been cut off from the Weave.
Knights of the Mystic Fire
Elite warriors in service to Mystra can join the Knights of the Mystic Fire. These knights lead Mystra's martial efforts and command lesser soldiers. With sword and spell, they protect her temples, defend sacred sites, and attack her enemies. Eldritch Knights, Bladesingers, Paladins, Rangers, and other characters who combine fighting skill with magic make excellent Knights of the Mystic Fire.
Individuals who seek to become a Knight of the Mystic Fire must prove themselves in service to Mystra. This service lasts several years and includes garrison duty guarding Mystra's temples, or it might involve membership in one of Mystra's lesser orders (such as the Order of the Shooting Star). Adventurers might prove themselves by questing on Mystra's behalf or defending the faithful from violent assaults.
To be made a knight, a candidate must display three qualities: they must be trusted by Mystra's priests, they must be an exemplary warrior, and they must display leadership. The candidate must hold an all-night vigil under the stars and swear an oath of loyalty to Mystra before being invested with the order's distinctive blue tabard marked with a fiery silver star. They often use a knightly honorific before their name, such as "Sir," "Lady," "Dame," and the like.
Knights of the Mystic Fire receive training in arcane and divine magic as well as fighting techniques. Knights are supported with a free Comfortable lifestyle at any temple of Mystra. With sufficient notice and cause, they can call on a task force of lesser warriors such as Guards, Knights, Scouts, or Warrior Infantry.
In addition to serving Mystra's priests, Knights of the Mystic Fire work alongside followers of Azuth, Kelemvor, and Selûne, traditional allies of Mystra. Their foremost enemy is Cyric and his followers; they defend against Cyric's plots and aggressively seek out his temples and shrines to destroy them.