Revenant

A knight wreathed in shadow stands above the bodies of her former comrades, their betrayal of her avenged as she pulls their souls into her helm. After a moment of horrifying screams, her helm clicks and fire erupts from her, transforming that shadow into flame. 

Revenants are creatures of vengeance, death, and unfinished business. They straddle the line between life and death, devoting themselves entirely to the law of steel. These fighters burn with hellfire and the chill of death, determined to live long enough to see their goals complete

Revenants are unfettered in their determination and unwavering in their resolve, often putting their own goals as their priority. That being said, they will be the first to pay back a debt, and will ensure that yours is not a business they leave unfinished.

Soul Devour

Beginning when you choose this archetype at 3rd level, you can use your reaction to take in the soul of a creature killed within the past minute. You can hold a number of souls equal to your proficiency bonus. While holding these souls, you have a bonus to your attack and damage rolls equal to the number of souls you hold. 

At the end of every long rest, you must make a DC 10+the number of souls in your possession CON saving throw or lose all the souls you hold.

Hell Touched

Starting at 7th level, you can burn souls to add 1d6 damage per soul. This damage type is either fire or cold which you can change with no souls left after a long rest. 

Starting at 11th level, this damage increases to 1d8 and again at 15th level to 2d6.

Fire and Ice

When you have no souls left, you may change your damage type after a long rest from fire to cold and vice versa.

Morbid Skills

At 10th level, your mastery of souls allows you to take skills from your souls, bolstering your own talents. You gain a bonus equal to the number of souls you possess to all ability checks and saving throws. Additionally, if you fail a check or saving throw, you can choose to burn one of your souls to gain an additional d6 to the roll. This bonus increases to a d8 at 15th level

Infernal Sacrifice

Starting at 15th level, you can burn one of your souls to regain a use of second wind which you can use as a free action on your turn. Additionally, once per long rest, when you are first dropped to 0 hp, you may use your reaction to instead sacrifice one of your souls and immediately use your second wind feature.

Great Wraith

At 18th level, you have gained a true mastery of souls. By expending all of your souls, you can cast either investiture of flame or investiture of ice depending on which element you have chosen. Additionally, while under the effects of one of these spells, you have resistance to nonmagical bludgeoning, piercing, and slashing damage. You also do not need to hold concentration on these spells and all of your attacks deal additional damage equal to holding one soul.