Greater doppelganger

Greater doppelgangers, also called Shallar, elder doppelgangers, or mirrorkin, were more powerful cousins of the common doppelganger. While a normal doppelganger could adopt the appearance of a person, a greater doppelganger could adopt their entire personality.

Description
Like regular doppelgangers, greater doppelgangers appeared as gangly, hairless, gray-skinned humanoids with pale eyes. However, they were faster and more agile than normal doppelgangers, and had tough, protective skin that could continue to protect them regardless of the form they assumed.

Abilities
They could adopt the shape and body of any humanoid between and  tall. They could further eat a humanoid's brain and, in doing so, absorb their entire personality for later use. This gave them the power to replicate a victim's memories, languages, abilities, and alignment, and to assume their form with perfect accuracy. A greater doppelganger could memorize three entire personalities in this manner without difficulty, but ran the risk of forgetting one if they strained themselves to memorize more. They had access to basic or important memories of the humanoids they had consumed even when not "wearing" the personality.

Personality
Greater doppelgangers were highly intelligent and sophisticated, and preferred to pursue complex plots that required them to penetrate political and social structures. They were talented liars and deceivers. Unlike ordinary doppelgangers, they had the intelligence and creativity to create novel appearances for themselves without the need to copy someone.

They referred to humans as "stinking ones," claiming that they smelled far worse than doppelgangers.

Combat
Greater doppelgangers preferred assassination over combat. They would use their powers of telepathy and mind reading to learn how to set victims at ease or to adopt the form of people they trusted, and then stab them in the back with their sharp claws. They were known to adjust the shape of their claws to make the wounds appear as conventional stab wounds in order to deflect suspicion.

In their natural form, greater doppelgangers attacked with their powerful fists or claws. While wearing the form of a humanoid whose brain they had consumed, the greater doppelganger had access to their combat abilities and skills, but could not replicate the spells or powers of clerics or paladins. They could be briefly shunted into their natural form if they behaved in a way that was strongly opposed to the alignment of the personality they were embodying.

Owing to their innate mastery of shapechanging magic, greater dopplegangers had the ability to twist and rend the power of similar magic in order to injure other creatures under the effects of any kind of polymorph spell.

They were immune to most mind-affecting magic&mdash;such as those which would hold them in place, put them to sleep, or charm them&mdash;and their alignment could not be detected. Even psionicists struggled to penetrate their mental defenses. Only the power of true seeing could reliably reveal them.

Society
They were rarely seen in their natural state. Most often, greater doppelgangers were encountered working alone, having adopted the form of someone important while in the middle of a complex scheme, and most adventurers would remain blissfully unaware that they had even crossed paths with the creature. They would occasionally also be found leading organizations or groups of lesser doppelgangers. They did not work well with others, especially not as a subordinate.

Greater doppelgangers were capable of bearing children. To do so, the greater doppelganger had to assume a female form and to maintain that form for the duration of a pregnancy, otherwise the unborn offspring would die.

History
Greater doppelgangers referred to themselves as "Shallar." The term "mirrorkin" was an ancient way of referring to them, but remained in usage in the Sword Coast as of the mid-to-late 14 century DR.

Beginning in the 1340s DR, an organization called the Unseen, led by nine greater doppelgangers, began operating in Skullport and Waterdeep. They had some success&mdash;and notable failures&mdash;in their efforts to infiltrate the power structures of Waterdeep. By the late–1360s DR they had successfully infiltrated a number of guilds and criminal organizations, including the Xanathar's Thieves' Guild, and had turned their attention to a scheme in which greater doppelgangers disguised as human women would conspire to sire illegitimate children with members of the Waterdhavian nobility. A greater doppelganger was involved in a plot to get close to the Open Lord of Waterdeep, Piergeiron the Paladinson, circa 1371 DR.

Notable Greater Doppelgangers

 * Hlaavin, a half-illithid greater doppelganger who led the Unseen in the mid-to-late 13 century DR.
 * Ptola, a member of the Unseen working to infiltrate as many of Skullport's factions as possible in the 1370s DR.
 * Rhelgyn, a member of the Unseen who assumed the identify of Lord Huld Belabranta.
 * Telakin, one of the nine leaders of the Unseen who was active in trying to control the Waterdhavian Dock Ward and City Watch in the 1370s DR.
 * Quelzard, an occasional patron of the Company of Crazed Venturers.