And far as Sharrians in the party, that is likely not an accident, but rather Shar's influence or one of her more powerful servants influence on events.
Pretty hefty quest spoiler re: Nightsong - It seems to be a person. A girl. And she may be a follower/companion with unique skills: |While in dim light or darkness, Nightsong can teleport as a bonus action up to 60 feet to an unoccupied space she can see that is also in dim light or darkness. She then has advantage on the first melee attack she makes before the end of the turn.|"
|Each creature must make a DC 14 Con ST, taking 3d8 necrotic damage on a failed save, or half as much damage on a successful one. If a humanoid is killed by this damage, an undead Shadow rises from its corpse and fights alongside Nightsong. Nightfall also extinguishes all lightsources|
And dialogue: "I am Nightsong, Shar's penitent. Cursed to bear the loss of all those who worship her." "I will always be Nightsong, but you can be something more. You're remembering." - Possibly related to Shadowheart.
Quest has multiple endings - you can give her to at least two or three different people, kill her, ignore her or free her of her curse.
So it seems to me the Nightsong is what Shadowheart would become as a "beautiful weapon" t. the Absolute.
I wonder how hard it would be to turn some of the chapter 1 followers into companions. We could use more good or potentially good companions in BG3.
This "Nightsong" almost sounds like a mutated Shadar Kai from the description. That's a racial option I would love to have as a PC race.. with +2 Dex, +1 Con, superior darkvision, and the teleport.
My understanding is this
she's very likely an avatar of Shar. One of her iconic lines is "Shar is the Nightsinger. And I am her Nightsong." A few other lines also point out that Shar might come back and control over her again if we don't play our cards right.
