Armor of Frost. A thin layer of hard ice covers the giant's body, granting it a base Armor Class equal to 16 + its Dexerity modifier. A creature that touches the giant or hits it with a melee attack while within 5 feet of it takes 5 (1d10) cold damage.

Freezing Weapons. Any melee weapon the giant wields deals an extra 5 (1d10) cold damage on a hit (included in the attack). 

Ice Walk. The giant can move across and climb icy surfaces without needing to make an ability check. Additionally, difficult terrain composed of ice or snow doesn't cost it extra movement.

Innate Spellcasting. The giant's innate spellcasting ability is Charisma (spell save DC 15, +7 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: ice knife, ray of frost, shape water
3/day each: cone of cold, ice storm
1/day each: freezing sphere, wall of ice

Legendary Resistance (3/day). If the giant fails a saving throw, it can choose to succeed instead.

Multiattack. The giant makes two greataxe attacks.

Greataxe. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 25 (3d12 + 6) slashing damage plus 5 (1d10) cold damage.

Rock. Ranged Weapon Attack: +10 to hit, range 60/240 ft., one target. Hit: 28 (4d10 + 6) bludgeoning damage.

The giant 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. The giant regains spent legendary actions at the start of its turn.

Detect. The giant makes a Wisdom (Perception) check.

Greataxe Attack. The giant makes a greataxe attack.

Snow Cyclone (Costs 2 Actions). Each creature within 30 feet of the giant must make a DC 15 Constitution saving throw against this magic, taking 10 (3d6) cold damage on a failed save, or half as much on a successful one. Additionally, the area within a 30-foot radius sphere around the giant is heavily obscured until the start of its next turn.