Way of Hailing Blows

Monks that train in icy tundra's, that have hardened themselves to the perpetual barrage of hail storms, and have learned to resist the biting chill of frost and snow, will eventually be able to become one with the storm. Monks of this discipline will harness the essence of frost and ice itself and channel that into their strikes. Their fists will be as relentless as hailstones, their skin as hard as ice, their fury like that of an avalanche. They are the storm incarnate.

Hailstone Strikes

At 3rd level when you choose this subclass you gain the ability to pelt your enemies with blows, like hailstones in a storm. When you use a ki point to make 2 flurry of blows attacks, you can expend an extra ki point to make an additional attack. You can do this a number of times equal to your level divided by 4 (minimum of 1) per turn, with each additional attack costing 1 ki point. In addition you gain resistance to cold damage.

Icicle Kunai

Starting at 6th level you have learned how to concentrate your ki down into corporeal form, creating small icicle-like kunai that can be flung at your enemies. You can spend 2 ki points to hurl a series of icicles at one creature of your choice. Make a ranged attack roll (you may use either your dexterity or wisdom modifier). On a hit the target takes piercing damage equal to 2 times your martial arts die and cold damage equal to 2 times your martial arts die.

Glacial Form

At 11th level you can become as formidable as a glacier. You can spend 3 Ki points as an action to change your body into an icy form of yourself. This form lasts for 1 minute, until you are knocked unconscious or until you drop it as a free action. Whilst in this form you have resistance to slashing and piercing damage, and you gain immunity to cold damage, however you have vulnerability to bludgeoning damage. Your unarmed strikes deal cold damage instead of bludgeoning. 

Whilst in this form your speed is reduced by 15 feet, however you do not suffer from difficult terrain created by heavy snow, ice or other cold and snowy environments. You emanate a 5 foot aura of freezing cold that chills any creature around you. If a creature ends its turn in this aura it must make a Constitution saving throw or take cold damage equal to one roll of your martial arts die. If you hit a target with your flurry of blows whilst in this form you reduce their speed to 0 until the start of your next turn. 

Additionally, whilst in this form you can use your Icicle Kunai ability without using Ki points.

Avalanche

At 17th level you wield the Force of an Avalanche. You can spend 4 Ki points to summon an avalanche to crush your enemies. The avalanche is 15 feet wide and travels up to 30 feet. Each creature in its path must make a Strength saving throw. On a failed save they take 4d8 bludgeoning damage and 4d8 cold damage and are knocked prone. If they succeed they take half as much damage and are not knocked prone. This entire area then becomes difficult terrain.