Innate Spellcasting.

The hag's innate spellcasting ability is Charisma (spell save DC 14, +6 to hit with spell attacks). She can innately cast the following spells, requiring no material components:

At will: detect magic, magic missile
2/day each: plane shift (self only), ray of enfeeblement, sleep

Magic Resistance.

The hag has advantage on saving throws against spells and other magical effects.

Night Hag Items.

A night hag carries two very rare magic items that she must craft for herself. If either object is lost, the night hag will go to great lengths to retrieve it, as creating a new tool takes time and effort.

Heartstone: This lustrous black gem allows a night hag to become ethereal while it is in her possession. The touch of a heartstone also cures any disease. Crafting a heartstone takes 30 days.

Soul Bag: When an evil humanoid dies as a result of a night hag's Nightmare Haunting, the hag catches the soul in this black sack made of stitched flesh. A soul bag can hold only one evil soul at a time, and only the night hag who crafted the bag can catch a soul with it. Crafting a soul bag takes 7 days and a humanoid sacrifice (whose flesh is used to make the bag).

Actions

Claws (Hag Form Only).

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) slashing damage.

Change Shape.

The hag magically polymorphs into a Small or Medium female humanoid, or back into her true form. Her statistics are the same in each form. Any equipment she is wearing or carrying isn't transformed. She reverts to her true form if she dies.

Etherealness.

The hag magically enters the Ethereal Plane from the Material Plane, or vice versa. To do so, the hag must have a heartstone in her possession.

Nightmare Haunting (1/Day).

While on the Ethereal Plane, the hag magically touches a sleeping humanoid on the Material Plane. A protection from evil and good spell cast on the target prevents this contact, as does a magic circle. As long as the contact persists, the target has dreadful visions. If these visions last for at least 1 hour, the target gains no benefit from its rest, and its hit point maximum is reduced by 5 (1d10). If this effect reduces the target's hit point maximum to 0, the target dies, and if the target was evil, its soul is trapped in the hag's soul bag. The reduction to the target's hit point maximum lasts until removed by the greater restoration spell or similar magic.

Lair Actions

The following lair actions are options for grandmothers and powerful aunties. Grandmothers usually have three to five lair actions, aunties usually only one (if they have any at all). Unless otherwise noted, any lair action that requires a creature to make a saving throw uses the save DC of the hag's most powerful ability.

On initiative count 20 (losing initiative ties), the hag can take a lair action to cause one of the following effects, but can't use the same effect two rounds in a row:

Until initiative count 20 on the next round, the hag can pass through solid walls, doors, ceilings, and floors as if the surfaces weren't there.
The hag targets any number of doors and windows that she can see, causing each one to either open or close as she wishes. Closed doors can be magically locked (requiring a successful DC 20 Strength check to force open) until she chooses to make them unlocked, or until she uses this lair action again to open them.

A powerful night hag might have the following additional lair actions:

One creature the hag can see within 120 feet of her must succeed on a DC 15 Charisma saving throw or be banished to a prison demiplane. To escape, the creature must use its action to make a Charisma check contested by the hag's. If the creature wins, it escapes the demiplane. Otherwise, the effect ends on initiative count 20 on the next round. When the effect ends, the creature reappears in the space it left or in the nearest unoccupied space if that one is occupied.
The hag targets up to three creatures that she can see within 60 feet of her. Each target must succeed on a DC 15 Constitution saving throw or be flung up to 30 feet through the air. A creature that strikes a solid object or is released in midair takes 1d6 bludgeoning damage for every 10 feet moved or fallen.

Regional Effects

Each hag's lair is the source of three to five regional effects; the home of a grandmother, an auntie, or a coven has more effects than the lair of a single hag, including some that can directly harm intruders. Any regional effect that requires a creature to make a saving throw uses the save DC of the hag's most powerful ability. These effects either end immediately if the hag dies or abandons the lair, or take up to 2d10 days to fade away.

The region within 1 mile of a grandmother hag's lair is warped by the creature's fell magic, which creates one or more of the following effects:

Birds, rodents, snakes, spiders, or toads (or some other creatures appropriate to the hag) are found in great profusion.
Beasts that have an Intelligence score of 2 or lower are charmed by the hag and directed to be aggressive toward intruders in the area.
Strange carved figurines, twig fetishes, or rag dolls magically appear in trees.

A powerful night hag creates one or more of the following additional regional effects within 1 mile of her lair:

Shadows seem abnormally gaunt and sometimes move on their own as though alive.
Creatures are transported to a harmless but eerie demiplane filled with shadowy forms, waxy corpses, and cackling. The creatures are trapped there for a minute or two, and then returned to the place where they vanished from.
Intelligent creatures see hallucinations of dead friends, family members, and even themselves littering the hag's realm. Any attempt to interact with a hallucinatory image causes it to disappear.