Shar

Creator of the Shadow Weave, Magic in opposition of Mystra's powers.
Shar, the Mistress of the Night, is the goddess of darkness and the caverns of Faerûn, as well as a neutral evil greater deity. Counterpart to her twin Mystra, she presides over caverns, darkness, dungeons, forgetfulness, loss, night, secrets, and the Underdark. Among her array of twisted powers was the ability to see everything that lay or happened in the dark.
The clergy of Shar were a secretive organization that pursued subversive tactics rather than direct confrontation with its rivals. In addition to her clerics, Shar maintained an elite order of sorcerer monks who could tap Shar's Shadow Weave.

Divine Domains

Caverns, darkness, dungeons, forgetfulness, loss, night, secrets, and the Underdark.
Shar's realm was originally on the Plane of Shadow and was a tower that had no obvious entrances called the Tower of Loss. She would trap those who enjoyed their freedom inside, savoring their despair at their loss, though she would allow petitioners and visiting worshipers to freely come and go (perhaps to further torture the trapped ones).
When she created the Shadowfell, Shar abandoned the Tower of Loss and created a new realm in the Astral Sea, larger than any of the others there. Among the dark scenery, with its black sand and shadowy natural features, lay the Towers of Night. Her new abode, a more palatial one than her old home, was built atop the tallest mountain of this realm. Access to the Shadowfell was easy from here.

Divine Symbols & Sigils

Shar's symbol was a black disk with a deep purple border.

Divine Classification

Dark Goddess

Church/Cult

Sharites

The Shadow Weave:

The Shadow Weave is a force of magic similar to the Weave. The Shadow Weave originates from Shar rather than from Mystra. Shar studied the Weave long ago, and created a dark distorted version of it, and it is said to lie in between the strands of the Weave. Though the Shadow Weave has existed for quite some time (at least several millennia), only in recent years has its use spread rapidly and become known.
A spellcaster who wants to manipulate the Shadow Weave must either worship Shar, permanently lose a piece of his or her mind,or make some sort of arrangement with Shar and his or her existing patron deity. A Shadow Adept is a spellcaster who specializes in using the Shadow Weave. The Shadow Weave is best suited for dark magic that drains life or muddles the mind and the senses, but less suited for magic that manipulates energy or matter. Spells from the schools of Enchantment, Illusion and Necromancy are enhanced, while those from the schools of Evocation and Transmutation are impaired. The Shadow Weave is also superior for fueling spells that create darkness (spells with the darkness descriptor), while it is impossible to use it to create light of any kind (spells with the light descriptor).
Since the Shadow Weave is a separate force of magic, it is not affected by areas of dead magic or wild magic within the Weave. An anti-magic field however counters all magic within its area, and that includes wielders of Shadow Weave magic. Shadow Weave users must also overcome any spell resistance a creature might have. It is harder for a Weave user to perceive, counter or dispel spells created by using the Shadow Weave, but at the same time it is also harder for a Shadow Weave user to affect spells created by using the Weave. Any magic item created using the Shadow Weave is a Shadow Weave item and affected by the same benefits and limitations as a Shadow Weave spell.