Magical Histories, Volume 1: The Origins of Mystra
To know of Mystra, the goddess of magic, we must first consider her earlier incarnations, beginning with Mystryl. The Lady of Mysteries was said to have come into existence during a conflict between the goddesses Shar and Selûne. In their efforts to best one another, the twin sisters of darkness and light inadvertently forged a portion of their opposing energies into a new being of pure magic - Mystryl. As an embodiment of magic, Mystryl laid claim to unparalleled control over the Weave - the very fabric by which magic could be channeled and harnessed - for it was but an extension of her being. For her, to use magic was as natural as it would be for another to draw a breath or curl their finger. It was in -339 DR that Mystryl gave way to Mystra, when the former had her powers seized by Karsus - a Netherese lord, and perhaps the most powerful and ambitious wizard to have ever lived. Yet Mystryl sought to deny him his ill-gotten prize - sacrificing herself so that for a moment, the Weave faltered, and all magic briefly ceased. Karsus's Folly brought about the destruction of Netheril and the end of his ambition. Yet the Weave would not go unattended for long. Within moments, the goddess of magic was reborn, as Mystra.