Armor Class 17 (natural armor)
Hit Points 91 (14d8 + 28)
Speed 30 ft., fly 50 ft.
Saving Throws WIS +4
Skills Nature +4, Perception +4, Stealth +6, Survival +4
Damage Immunities cold
Senses darkvision 60 ft., passive Perception 14
Languages Auran, Common, Giant
Challenge 7
Control Weather (1/Day). The hag can cast the control weather spell, requiring no material components and using Charisma as the spellcasting ability.
Graystaff Magic. The hag carries a graystaff, a magic staff. The hag can use its flying speed only while astride the staff. If the staff is lost or destroyed, the hag must craft another, which takes a year and a day. Only a bheur hag can use a graystaff
Ice Walk. The hag can move across and climb icy surfaces without needing to make an ability check, and 3 composed of ice or snow doesn't cost the hag extra moment.
Multiattack. The hag makes two Slam or Frost Shard attacks.
Slam. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 10 (2d8 + 1) bludgeoning damage plus 18 (4d8) cold damage.
Frost Shard. Ranged Spell Attack: +6 to hit, range 60 ft., one target. Hit: 30 (6d8 + 3) cold damage, and the target's speed is reduced by 10 feet until the start of the hag's next turn.
Horrific Feast. The hag feeds on the corpse of one enemy within reach that died within the past minute. Each creature of the hag's choice that is within 60 feet and able to see the feeding must succeed on a DC 15 Wisdom saving throw or be frightened of the hag for 1 minute. While frightened in this way, a creature is incapacitated, can't understand what others say, can't read, and speaks only in gibberish. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the hag's Horrific Feast for the next 24 hours.
Mordenkainen Presents: Monsters of the Multiverse, p. 62