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/ Hag Coven/ Hag Eye. See Monster Manual
Shared Spellcasting (Coven Only). While all three members of a hag coven are within 30 feet of one another, they can each cast the following spells from the wizard's spell list but must share the spell slots among themselves: 1st level (4 slots): identify, ray of sickness. 2nd level (3 slots): hold person, locate object. 3rd level (3 slots): bestow curse, counterspell, lightning bolt. 4th level (3 slots): phantasmal killer, polymorph. 5th level (2 slots): contact other plane, scrying. 6th level (1 slot): eye bite
For casting these spells, each hag is a 12th-level spellcaster that uses Intelligence as her spellcasting ability. The spell save DC is 12+the hag's Intelligence modifier, and the spell attack bonus is 4+the hag's Intelligence modifier.
Claws (Hag Form Only). Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: (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.