Legendary Resistance (3/Day). If Yskaldor fails a saving throw, he can choose to succeed instead.

Aura of Winter. Yskaldor radiates an aura of extreme cold in a 30-foot radius. Creatures that start their turn within the aura must make a DC 22 Constitution saving throw, taking 35 (10d6) cold damage on a failed save, or half as much on a success. The area within the aura is considered difficult terrain, and water freezes instantly.

Innate Spellcasting. Yskaldor’s spellcasting ability is Charisma (spell save DC 23, +15 to hit with spell attacks). He can innately cast the following spells, requiring no material components:

• At will: Ice Storm, Cone of Cold, Control Weather
• 3/day: Wall of Ice, Chain Lightning, Greater Invisibility
• 1/day: Storm of Vengeance, Control Winds, Plane Shift (self only)

Regeneration. Yskaldor regains 30 hit points at the start of his turn if he has at least 1 hit point and isn't in direct sunlight. If Yskaldor takes fire damage, this trait doesn't function at the start of his next turn.

Godly Strength. Yskaldor can lift, push, or pull up to 150 tons, and his melee attacks are considered magical.

Multiattack. Yskaldor makes three attacks: one with his greataxe and two with his Fist of Winter.

Greataxe of Eternal Frost. Melee Weapon Attack: +18 to hit, reach 15 ft., one target.
Hit: 36 (4d12 + 10) slashing damage plus 18 (4d8) cold damage. If the target is a creature, it must succeed on a DC 23 Constitution saving throw or be paralyzed by extreme cold until the end of its next turn.

Fist of Winter. Melee Weapon Attack: +18 to hit, reach 10 ft., one target.
Hit: 28 (4d8 + 10) bludgeoning damage plus 18 (4d8) cold damage. The target must succeed on a DC 22 Constitution saving throw or suffer disadvantage on attack rolls and saving throws until the end of Yskaldor's next turn.

Breath of the Frost God (Recharge 5-6). Yskaldor exhales an icy blast in a 90-foot cone. Each creature in the area must make a DC 23 Constitution saving throw, taking 88 (16d10) cold damage on a failed save, or half as much damage on a successful one. Creatures who fail the saving throw are also restrained as ice forms over them. They can repeat the saving throw at the end of each of their turns to end the effect.

Yskaldor can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. Yskaldor regains spent legendary actions at the start of his turn.

• Move. Yskaldor moves up to his speed without provoking opportunity attacks.
• Icy Gaze (Costs 2 Actions). Yskaldor targets one creature he can see within 60 feet. The target must succeed on a DC 23 Wisdom saving throw or be paralyzed with fear until the end of Yskaldor's next turn.
• Frost Nova (Costs 3 Actions). Yskaldor releases a burst of freezing energy. Each creature within 20 feet must make a DC 23 Constitution saving throw, taking 45 (10d8) cold damage on a failed save, or half as much on a successful one. The area becomes coated in ice, turning it into difficult terrain for 1 minute.

If Yskaldor’s hit points are reduced to 0 for the first time, he taps into the full power of the winter storm, gaining the following effects:

• Mythic Awakening. Yskaldor regains 250 hit points.
• Endless Winter. The area within a 500-foot radius becomes engulfed in a blizzard for the rest of the battle. The storm imposes disadvantage on ranged attack rolls, and creatures take 10 (3d6) cold damage at the start of each of their turns.