Thuellai

Chilling Presence. At the start of each of the thuellai's turns, each creature within 15 feet of it must succeed on a DC 17 Constitution saving throw or take 7 (2d6) cold damage. For each minute a creature spends within 15 feet of the thuellai, it must succeed on a DC 17 Constitution saving throw or suffer one level of exhaustion from cold exposure. Unprotected, nonmagical flames within 15 feet of the thuellai are extinguished. Any spells of 3rd level or lower that provide resistance to cold damage and that are within 15 feet of the thuellai immediately end. Water freezes if it remains within 15 feet of the thuellai for at least 1 minute.

Elemental Nature. The thuellai doesn't require air, food, drink, or sleep.

Snowsight. The thuellai can see through areas obscured by snowfall, sleet, rain, and other wintry precipitation without penalty.

Multiattack. The thuellai makes three Icy Claw attacks.

Icy Claw. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) slashing damage plus 10 (3d6) cold damage.

Freezing Breath (Recharge 5-6). The thuellai exhales an icy blast in a 60-foot cone. Each creature in the area must make a DC 17 Dexterity saving throw, taking 49 (14d6) cold damage on a failed save, or half as much damage on a successful one.