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, [Tooltip Not Found], gate (Abyss only)

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

Claws.(Hag Form Only). Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 18 (2d8 + 4) slashing damage and the target is poisoned.

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.

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

Nightmarish Gateway (1/Day). While on the Abyssal Plane, the hag magically touches a 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 8 (1d10). If this effect reduces the target's hit point maximum to 0, the target dies and is used to open a gateway to the Abyss for 3 hours for each 8 hit points reduced. Lesser demons can come through, along with greater demons. There is a temporary portal to the Abyss which blights all land for 10 days and humanoids either get sick or corrupted by evil energies. 

One demon is empowered with abyssal energies and transforms into a minor demon lord, with all other demons near it compelled to serve as warriors.