The Revenant

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Level 3: Emanation of Winter

As a bonus action, you conjure spirits from the Elemental Planes that flit around you in a 15-foot Emanation for 1 minute. Until the emanation ends, any attack you make deals an extra 2d8 cold damage when you hit a creature in the Emanation. This damage adds a d8 at levels 5, 7, 10, and 15.

In addition, the ground in the Emanation is Difficult Terrain for your enemies.

You can do this a number of times equals to your proficiency bonus.

Level 3: Armour of Frost

When you deal damage to a target with cold damage or reduce a creature to 0 hit points with an attack, you gain one layer of Frost Armor. You can have a maximum number of layers equal to your Proficiency Bonus. Your layers last for 1 minute, or until you take a short or long rest.
Mechanics & Benefits
• AC Bonus: Every even numbered stack grants a +1 to AC.
• Damage Reduction: Whenever you take bludgeoning, piercing, or slashing damage, the damage is reduced by an amount equal to the number of Frost Armor layers you currently have.
• Losing Layers: Every time you take damage from an attack, you lose 1 layer of Frost Armor after the damage is resolved.
• Maximum Stacks Benefit: If you are at your maximum allowed layers of Frost Armor, you also gain resistance to Cold damage.

Level 7: Shield of the Winters Wrath

At level 7 you improve your defensive capabilities, you can now cast shield as a reaction a number of times equal to your proficiency bonus. 

• Reaction, which you take when you are hit by an attack roll or targeted by the Magic Missile spell. An imperceptible barrier of magical force protects you. Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from Magic Missile.

Alternatively, if your shield wouldn't stop the damage, you may instead use Winters Wrath.

• As a reaction, you may consume a charge of second wind to heal for a 1d6+ half your fighter level and fire off 2d8 cold damage at the creature that damaged you, taking half as much on a successful Dexterity saving throw. The DC for this is 8+Con+Prof.

Additionally, you gain an extra 2 charges of Second Wind now, and an additional 2 at level 18.

Level 10: Emanation; Blizzard

Once per short-rest, freeze a massive area, slowing and eventually stunning all enemies inside. While buffing allies inside the radius.
As an action you hurl a cryo-grenade to a point within 30 feet. A 30-foot-radius sphere centered on that point becomes difficult terrain for 3 turns. Any enemy that starts its turn in the area must make a Constitution saving throw.
Enemies
• Failed Save: Takes 4d6 cold damage and is Restrained.
• Successful Save: Takes half damage and is slowed by half their speed.
• If a creature fails its save two turns in a row while inside the blizzard, it becomes Paralyzed (Frozen) for 1 minute or until it takes fire damage.
Allies
• Heal for 1d4 plus your constitution modifier immediately and at the start of their turn if still in the radius.
• Have their move speed increased by 5 feet. 

Level 15: Cryogenic Critical

Your attack rolls with weapons while within Emanation of Winter can now score a Critical Hit on a roll of 18–20 on the d20.

Cold damage you deal now ignore resistance, if you have the Elemental Adept: Cold feat you additionally ignore immunity to cold damage.

Level 18: Winter Survivor

You attain the pinnacle of resilience in battle, giving you these benefits.

Improved Frost Armour: At the start of each of your turns, you regain Hit Points equal to 5 plus your Constitution modifier if you are Bloodied, have at least one stack of frost armour and have at least 1 Hit Point.
Winters Wrath: You may now add your full fighter level to the roll of your second wind when using Winters Wrath