Bride of Strahd. While Strahd can take Lair Actions, Anastrasya can benefit from them. If Strahd chooses his first Lair action, Anastrasya can pass through solid walls, doors, ceilings, and floors as if they weren't there. She only has this ability so long as Strahd allows her to have it.

Regeneration. Anastrasya regains 15 hit points at the start of her turn if she has at least 1 hit point and isn't in sunlight or running water. If she takes radiant damage or damage from holy water, this trait doesn't function at the start of her next turn.

Spider Climb. Anastrasya can climb difficult surfaces including upside down on ceilings, without needing to make an ability check.

Vampire Weaknesses. Ludmilla Vilisevic has the following flaws:
Forbiddance: Anastrasya can't enter a residence without an invitation from one of the occupants.
Harmed by Running Water: Anastrasya takes 20 acid damage when she ends her turn in running water.
Stake to the Heart: Anastrasya is destroyed if a piercing weapon made of wood is driven into her heart while she is incapacitated in her resting place.
Sunlight Hypersensitivity: Anastrasya takes 20 radiant damage when she starts her turn in sunlight. While in sunlight, she has disadvantage on attack rolls and ability checks.

Multiattack. Anastrasya makes two attacks, only one of which can be a bite attack.

Claws. Melee Weapon Attack: +6 to hit, reach 5ft., one target. Hit 8 (2d4 + 3) slashing damage. Instead of dealing damage, Anastrasya can grapple the target (escape DC 13).

Bite. Melee Weapon Attack: +6 to hit, reach 5ft., one willing creature, or a creature that is grappled by the vampire, incapacitated, or restrained. Hit 6 (1d6 + 3) piercing damage plus 7 (2d6) necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and Anastrasya regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Charm. Anastrasya targets one humanoid she can see within 30 feet of her. If the target can see Anastrasya, the target must succeed on a DC 16 Wisdom saving throw against this magic or be charmed. The charmed target regards Anastrasya as a trusted friend to be heeded and protected. The target isn't under Anastrasya's control, but it takes Anastrasya's requests and actions in the most favorable way and lets Anastrasya bite it.
Each time Anastrasya or his companions do anything harmful to the target, it can repeat the saving throw, ending the effect on itself on a success. Otherwise, the effect lasts 1 hour or until Anastrasya is destroyed, is on a different plane of existence than the target, or takes a bonus action to end the effect.

Children of the Night (1/day). Anastrasya magically calls 1d4 swarms of bats or swarms of rats, provided that the sun isn't up. The called creatures arrive in 1d4 rounds, acting as allies of Anastrasya and obeying his spoken commands. The beasts remain for 1 hour, until Anastrasya dies, or until she dismisses them as a bonus action.

Villain Actions - Once as specified at end of 1 PC's turn

Round 1: Charm. Anastrasya may immediately use her charm ability, as listed above.

Round 2: Misty Movement. Anastrasya takes the form of a cloud of mist and may move up to her speed without provoking attacks of opportunity. This ability does not function if she is in bright sunlight.

Round 3: Bride of the Ancient: Anastrasya can force others to experience Strahd's power. The target must make a Intelligence saying throw or be affected by the spell Phantasmal Force. The Target sees an illusion of Strahd attacking them.

Collective Villain Actions

When all three Brides of Strahd are together they take they gain the following Villian Actions.

Round 1: First Bride. Ludmilla casts Haste on both of the other Brides. The casting does not consume a spell slot but does take her concentration.

Round 2: The Night Creatures. Anastrasya summons 1d4 swarms of bats per the vampire ability. If the fight is in Castle Ravenloft the summoning is instant.

Round 3: Share in the Blood Lust. Volenta lets out a horrible cry that brings out the beast in her fellow vampires. All three may instantly take the attack action against any creature within 5 feet.