Demon Weave

The Demon Weave was a magical fabric that the goddess Lolth attempted to create in order to make herself the new goddess of arcane magic after the demise of Mystra.

Nature of the Demon Weave
The Demon Weave coexisted with the torn remains of Mystra's Weave that Mystra and her servants were trying to restore once she herself had been restored by Elminster in 1479 DR. The Demon Weave drained both power and stability from Mystra's Weave but Lolth had not managed to make it sustain itself in the way that Mystra's Weave could before the Spellplague and upon its restoration after the end of the Sundering. Therefore, the Demon Weave relied on the existence of Mystra's Weave in order to function and should Mystra's Weave have ever completely ceased to be, so too would the Demon Weave.

Those that Lolth allowed to use the Demon Weave could access arcane magic just as reliably as they could before the Spellplague but few knew that it required the efforts of individuals such as Elminster, Storm Silverhand, the Srinshee, and many others working under Mystra's auspices to bolster both Mystra's Weave and thereby ensure the survival of the Demon Weave.

History
In 1480 DR, Lolth sent her avatar, Danifae Yauntyrr, to the cities of the drow to task them with recovering items to fuel the creation of her new Weave. Those who obeyed traveled to the surface, scouring the land for ancient items from before the Spellplague, relics that were sacred to Mystra, sources of primordial energy, and sites of magical power. Those drow would then channel the power of those items and places to their goddess.

The first effect of this was, that in the spring of 1484 DR, drow wizards led by Tsabrak Xorlarrin would use the power gained from the new Weave to create magical darkness over large areas of land on the surface so they could comfortably exist there, even in the light of the sun. More and more of these areas of darkness appeared on the surface lands over the next year-and-a-half - this was known as the Darkening. Eventually though, in the fall of 1485 DR, a party of adventurers from Luruar descended into the ruins of Eryndlyn, where they helped a resurgent Mystra take command of the Demon Weave. She then began using it to strengthen her own resurgent Weave to restore it closer to the condition it was in before the Spellplague.

Notable effects

 * House Jaelre's attack on Shadowdale: Valan Jaelre attempted to steal and channel the power of the Pendant of Ashaba in order to weaken Shadowdale for a full invasion.
 * Drow political strife : By Lolth's will, arcane spellcasters in drow society (most of whom were male) found their social status elevated to that of drow females. Those who favored the status quo refused to follow Lolth's edicts, causing conflict that was further manipulated by the Jaezred Chaulssin.
 * The Darkening: As well as making life on the surface easier for drow, the magical darkness covering the land inspired many evil humanoids and monsters to become bolder. Several tribes of orcs, for example, split off from Many-Arrows to lay siege to Mithral Hall, Citadel Adbar, and Sundabar.