Mother Night is one of the The Three powers of Barovia, an ancient and powerful being bound to the land of Barovia and to the Amber Temple.

She is the goddess of dreams, divination and lycanthropy.

She is depicted by the Megaliths near Old Bonegrinder to have, along with the Root/Worlds/Barovia/NPCs/Morninglord, dwellled in the mythical Four Cities at the beginning of time.

Her power is split between the Stone of Sight and Madam Eva and a small amount is in Esmerelda d'Avenir

For many years, she has been bound to a human body, joined with the human woman Lysaga to become Baba Lysaga, a powerful and innately magical being. Over the centuries, Lysaga and Mother Night had become so intertwined that they consider themselves to be one being.
 
Mother Night is also worshiped by several of the other beings of Barovia, such as the coven of hags, Morgantha's Coven residing at the Old Bonegrinder mill. These hags desecrated a holy site of the Root/Worlds/Barovia/NPCs/Morninglord, using the blood and teeth of slaughtered children to convert the shrine into a holy site of Mother Night.

Her presence is said to have manifested the most during the night, between dusk and dawn, but most Barovians think her, like the Root/Worlds/Barovia/NPCs/Morninglord, to have forsaken them. "The Devil Strahd" is commonly thought to have been chosen by her as a champion to punish the Barovian people for the sins of their familial progenitors. Thus, Mother Night is mostly venerated today by unnatural monsters and other creatures of the night.

Worshipers

As previously mentioned, a number of creatures venerate Mother Night:

• Baba Lysaga has been a faithful devotee even before the birth of Strahd. As revenge forexile, Lysaga petitioned, prayed, and sacrificed to Mother Night to strike Queen Ravenovia van Roeyen down with disease. Mother Night finally granted after many years of Lysaga's devotion. Lysaga continues ritualblood sacrifice to this day in the ruins of Berez, to where she wards off both the toll of time to her person and the use of divination magic against her.
• A werewolf pack loyal to Strahd call themselves the Children of the Mother Night, for they hold her in deep veneration. Strahd is mistakenly seen as Mother Night's personal champion, so they hold him in high regard and operate as his agents. The Children have a shrine to Mother Night in the Werewolf Den west of Lake Baratok

Marina

The current "Baba Lysaga" is actually Marina

Mother Night 1’s identity is, admittedly, irrelevant to the narrative of this campaign, However, her divine portfolio—including witches, foresight, nocturnal beasts, and lycanthropes—most closely matches that of Shar, the Forgotten Realms' greater god of trickery and death. Known also as the “Mistress of the Night,” Shar was the creator of the Shadowfell, the realm in which Barovia—and all the Demiplanes of Dread—now reside.

The Coven of Mother Night 1

Though most Barovians worship the Root/Worlds/Barovia/NPCs/Morninglord in public, a precious few scorn his faith and instead turn their worship to Mother Night 1, seeking safety, power, or simple vengeance.

Witches and werewolves comprise the bulk of Mother Night 1’s followers, though some ordinary Barovians build secret shrines to her, joining in profane fellowship with the creatures of night.