Lady Ada Mistborn

Background
Lady Ada Mistborn is one of the eldest daughter of Lord Janice Mistborn, and elder sister to Lady Eloithe Mistborn. After the death of the late Lady Elizabeth Nandar, she is said to take the throne of Nightstone.

She is also, as revealed by Eloithe's discovery, the distant relative of Lord Strahd.

Interactions with Mystic Obscura
While investigating the Vampire that had turned Dissumusk's friends, the adventuring party learned that the vampire responsible is none other than Lady Eloithe's sister.

Upon learning of their discovery, Lady Ada travelled to The Blue Tailed Mermaid - Inn and sought to kill Mystic Obscura. Upon entering, she disguised herself as Plink and searched for party members. However, she only found Arannis.

Pretending to be Plink, he seemed confused as she questioned him, and upon realising she and he were alone, pushed him out of the window. Arannis managed to hang onto the edge as Lady Ada declared that she should have killed them long before. Watching as Arannis dropped, Ada became Adrie before looking out again. After attempting to trick Arannis, but failing, she moved to Charm him and found herself unable to do so.

Arannis told her he had a message for her; suspecting it to be Ada from what he had just experienced, and drew out a Silver Chain that seemed to make her falter slightly. Before she could react, she was hit with a Fireball from the Moon Elf, and found her disguise gone. Feeling threatened as Arannis began to run off, she turned into bats and headed for her families house.

Upon finding Mystic Obscura in her Father's house, along with their brother, she subtly threatened Eloithe, Balasar and Aegon by revealing she was working with Agronak; Aegon's brother, and Parthinia Quell (who she was also in a relationship with), the woman who murdered all of Balasar's tribe, along with threatening her own family. She stated she would see them all in the North.

Eventually, Ada killed their father and disavowed both Eloithe and Edrick as Mistborn's. She then set to work as the only Mistborn left. However, it was revealed she had a daughter with Cassian, who she had tried to convince to come with her, only to be rejected by Briar and left in Last Light, within the High Forest.

Lady Eloithe Mistborn
Lady Ada seemed to have no qualms over killed Eloithe, despite being her sister. She even stated to Arannis that she should have killed them all; including Eloithe, as she attempted to kill him.

Parthinia Quell
Ada and Parthinia were reportedly in a relationship, both being merciless killers, seemingly fitting. Ada seemed unsettled by Arannis having the chain with both Ada's and Parthinia's initials in it, seemingly a lovers chain.