Thallan Shara (the Masked One)

Thallan Shara (known to the members of the Guild as "the Masked One") is an entity of unknown age and race who was previously trapped in Invis Winterenvy Sr's Mirror of Life Trapping. 

Relatively little is known about Shara prior to their entrapment in the mirror. Rumors and hearsay name them as a priest of Amaunator, one who committed some sin so vile they were not only banished from the Temple they served, but excommunicated and their name made heresy to speak. This has not been verified, but what is known is that they arrived as a nameless wanderer sometime roughly 250 years prior to present day, where they named themself a priest of Waukeen and pretended to serve that Temple faithfully before enacting a plan to destroy the city. 

It is unclear what Shara's plan to destroy Neverwinter was. Records of the city prior to the Great Fire have largely been lost, and what remains in the Archives is piecemeal and difficult to put together. What is known is that Shara bore some grudge against Artin Winterenvy, supposedly vowing to destroy the Winterenvy line as well as the city they helped found, before being trapped in the mirror. 

Thallan Shara was freed from Artin Winterenvy's Mirror of Life Trapping during a mission to help Andrew Bowditch retrieve said mirror from the Neverwinter Gentlefolk Society, where a would-be member of said society had been trapped. Choosing to break the mirror, members of the Guild saw those trapped within it -- all powerful, dangerous enemies of the Winterenvy family, most of whom had tried to murder various Winterenvy family members over the years, or else tried to lay waste to the city -- freed. Thallan Shara was one of those freed, seen as a person of unknown age/race/gender, wearing a wooden mask that seemed to be a mockery of those worn by the Masked Lords of Waterdeep. They thanked the party for freeing them from their prison before inquiring as to their motives in freeing them. When they discovered that the party was uninterested in helping them destroy the city of Neverwinter, they summoned several fire elementals before teleporting away. 

After their release, Undead activity along the Sword Coast began to increase, beginning with the finding of a ritual site outside of Helm's Hold, and culminating in the summoning of a Death Knight in the Far North, one that was destroyed by members of the Bounty Hunter's Guild. While it is unclear what end Shara is working toward, they appear to be partnered with a handful of people, including a priestess of Talona (goddess of plague and disease) to create a plague that will weaken Neverwinter, leaving it defenseless against the destruction they wish to sow. 

Members of the Guild have worked to find out who it is that Thallan Shara is, and what it is they desire most, but work to uncover what problem they have with the Winterenvy family or why they wish to see Neverwinter destroyed has been largely fruitless.