Frost Magic

Some sorcerers attune themselves to certain primordial elements, but none commit so fully as the Frost Sorcerer.

Your sorcerous powers may have been attained through a number of different ways. Your bloodline could have been subject to an ancient curse or blessing placed by a powerful frost giant or white dragon. You may have struck a bargain with one of these creatures in a bid for power, or for a chance at survival in the face of unbearable cold. Perhaps you were simply born in an unusually bitter winter, and were marked from birth to live with a frozen heart.

However you came upon your power, you use it to it's full effect to shield yourself with unbreakable permafrost, flash freeze your foes in their tracks, and shatter them like the very ice you control.

Frozen Heart

Born with ice in your veins, your magic is infused with the frigid cold of the arctic wastes.

Starting when you choose this origin at 1st level, you become resistant to cold damage. Additionally, you may harness your frozen nature to alter the essence of spells you cast. At the end of a long rest you may choose fire, acid, lightning, thunder, or poison damage. Until the end of your next long rest, spells dealing that type of damage now deal cold damage instead.

You also choose to learn either the Control Water cantrip or the Ray of Frost cantrip, neither of which count against the total amount of sorcerer cantrips you know.

Ray of Frost

You learn the Ray of Frost cantrip which doesn't against the total amount of spells you can learn.

Shape Water

You learn the Shape Water cantrip which doesn't against the total amount of spells you can learn.

Magical Frostbite

Starting at 1st level, you learn to suffuse your cold magic into your enemies to debilitate and slow them. Whenever you damage a creature with cold damage, you may force them to make a Constitution saving throw equal to your spell save DC. If they fail, the creature's movement speed is halved and they have disadvantage on Dexterity saving throws for the next minute. At the end of the creatures turn it may repeat the saving throw, ending the effect on a success. A number of creatures equal to your proficiency modifier may be affected by your Magical Frostbite at once, you may dismiss the effect against any number of creatures at will on your turn (requires no action). A creature is immune to this effect if they are immune to cold damage.

Armour of the Tundra

Starting at 6th level, you learn to use rock hard permafrost to shield you and keep you frozen steadfast to the ground in the face of pressure. As an action, you may spend 3 sorcery points to don Armour of the Tundra. While equipped, you can choose to ignore forced movement while connected to a solid surface, you ignore difficult terrain caused by snow or ice, you can choose to freeze the water beneath you as you walk on it, and your AC becomes 14 + your dexterity modifier. The armour lasts for 8 hours, or until dismissed (no action required).

Blizzard Aura

Starting at 14th level, you become immune to cold damage, and you become so attuned to cold magic that you summon harsh gusts of wind and flurries of snow around you while casting spells. Whenever you cast a spell which deals cold damage, you may choose to make the 10 ft radius surrounding you difficult terrain to all creatures except those immune or resistant to cold damage until the start of your next turn. If your Armour of the Tundra is equipped, the radius is increased to 30 ft, creatures affected are no longer able to make attacks of opportunity. 

Eternal Frostbite

Starting at 18th level, your frost magic is so potent that the hearts of those effected may become trapped in ice eternally. When a creature fails their saving throw against your Magical Frostbite ability, you may spend 6 sorcery points to Petrify it as ice for 1 minute. You may choose to occupy your concentration on this petrification the same way you would a concentration spell. If you stop concentrating on it, the petrified creature may repeat the saving throw against your magical frostbite at the end of it's turn.

After 1 continuous minute of being petrified in this way, the creature remains petrified indefinitely. It can be cured by a 9th level Greater Restoration or a Wish spell. If the creature is killed while petrified their body is shattered, and cannot be resurrected or raised as undead beyond the use of a True Resurrection or Wish spell.