Moytirra
Moytirra was one of the most powerful Avataras of Mazzarin's age. She founded the Warlocks of the Scholomance and even was powerful enough to challenge Mazzarin himself.
The Avatara opened their school to anyone who were interested in the magical arts, attracting the attention of Moytirra. She was noted for her fevered studies and lust for power. She gathered many followers who shared the same views and they conducted rituals to convene with the Dark Gods, forbidden by the Avatara. Mazzarin, Archmage and founder of the Avatara of Illuan, confronted Moytirra about this. Moytirra zealously defended her actions, believing that power is worth any cost, even the soul. A duel was fought between them and, despite both being equally skilled in the ways of magic, Mazzarin emerged the victor. Mazzarin bid Moytirra to end her pursuit of dark magic or be exiled from the ranks of the Avatara. Moytirra cursed at Mazzarin for her defeat and she and her followers left the Avatara.
In time, Moytirra founded her own school of magic and the Order of Scholomance was born.
It is unknown of what became of Moytirra, but such a powerful mage that managed to challenge Mazzarin would unlikely just disappear. A bigger mystery is why her Warlock order followed Mjarin and then Mydred if she was still around. Perhaps she died, but that is subject to conjecture since such an important being would have likely been mentioned in the Total Codex or would have been discussed about in the journal.
Moytirra also would have been sought after by the Dark--whether to be raised as an undead or for her ability to command the Warlocks. What became of her, where she is, and where her loyalties truly lie are a mystery.
Powers
Moytirra could utilize many fire dreams, mentally debilitating dreams, teleportation spells, transforming dreams (units into small meaningless animals), Moytirra could fly over long distances, and she could use most spells that were darker versions of Mazzarin's spells.