Agrabotha the Tainted Night Hag

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, hold person, ray of frost

2/day each: plane shift (self only), ray of enfeeblement, sleep

3/day each: cone of cold, ice storm, wall of ice

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: 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.

Consume Spell. As a reaction after failing a saving throw, the Hag can choose to succeed. 3/day, all charges restored after a long rest. The spell has no effect and the Hag regains hp equal to the level of spell consumed. 

The hag can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The hag regains spent legendary actions at the start of its turn

Frightful Gaze:  The hag turns a single eye to a creature in front of her within 60ft. The creature must succeed on a DC 14 WIS saving throw or be frightened until the end of their next turn. 

Wicked Step: The hag teleports up to 30ft into an unoccupied space. In the space she just left behind noxious gas fills the area. Any creatures within 5ft must make a DC 14 CON saving throw or spend their next action vomiting violently. 

Noxious Burp: The Hag exhales an acid onto all creatures in a 15ft Cone in front of her. Creatures must make a DC 14 Dex Save or take 3d10+5 Acid Damage. Recharge on a 6 of 1d6.

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