Legendary Resistance (6/Day).

If the scion fails a saving throw, it can choose to succeed instead.

Magic Resistance.

The scion has advantage on saving throws against spells and other magical effects.

Siege Monster.

The scion deals double damage to objects and structures.

Actions

Multiattack.

The scion makes one Ice Axe and two Slam attacks, or it makes two Glacier Throw attacks.

Ice Axe.

Melee Weapon Attack: +17 to hit, reach 30 ft., one target. Hit: 36 (4d12 + 10) force damage plus 18 (4d8) cold damage.

Slam.

Melee Weapon Attack: +17 to hit, reach 20 ft., one target. Hit: 32 (4d10 + 10) force damage.

Glacier Throw.

Ranged Weapon Attack: +17 to hit, range 120/480 ft., one target. Hit: 36 (4d12 + 10) bludgeoning damage plus 14 (4d6) cold damage, and the target must succeed on a DC 25 Strength saving throw or have the prone condition.

Glacial Upheaval (Recharge 5–6).

The scion digs its hands into the ground at a point it can see within 30 feet of itself and launches a magically conjured mass of ice into the air. Each creature other than the scion in a 30-foot-radius, 100-foot-high cylinder centered on that point must make a DC 25 Dexterity saving throw. On a failed save, a creature takes 36 (8d8) bludgeoning damage plus 19 (3d12) cold damage and is pushed vertically to the top of the cylinder, at which point the creature falls. On a successful save, a creature takes half as much damage and is pushed to the nearest unoccupied space outside the cylinder with no additional effects.

At the start of the scion's next turn, a mass of ice plummets to the ground on a point the scion can see within 60 feet of the point the scion dug its hands into. Each creature in a 30-foot-radius, 100-foot-high cylinder centered on that point must succeed on a DC 25 Dexterity saving throw or take 18 (4d8) bludgeoning damage plus 18 (4d8) cold damage.

Bonus Actions

Earth-Shaking Movement.

The scion moves up to its speed and sends a shock wave through the ground in a 60-foot-radius circle centered on itself. Each creature on the ground in that area that is concentrating must succeed on a DC 25 Constitution saving throw or lose concentration.

Regional Effects

The region surrounding a scion of Thrym is altered by the giant's magic, creating one or more of the following effects:

Biting Chill. Extreme cold envelops the land within 6 miles of the scion (see the Dungeon Master's Guide for rules on extreme cold). If the climate in the area already features extreme cold, the cold is numbing—creatures in the area without immunity or resistance to cold damage have disadvantage on Strength and Dexterity checks.
Empowered Frost Giants. Frost giants within 1,000 feet of the scion gain a +7 bonus to attack and damage rolls.
Thriving Wildlife. Beasts reproduce rapidly and thrive within 6 miles of the scion.

If the scion dies, these effects end immediately.

Scion of Thrym