DoomKnight (5e Subclass)
From D&D Wiki
Feared throughout the history of time, DoomKnights show little remorse for the living—sympathy is only derived from brute force. DoomKnights are the elite soldiers of the Shadowscythe army, pledging their undying allegiance to the Empress of Shadowfall, Gravelyn. Those who have chosen to follow the way of Evil may become a DoomKnight after proving their loyalty to Empress Gravelyn. 
- Dark Wound
Starting at 3rd level, your melee weapon attacks infect the wound left behind with dark energy, creating a Dark Wound. Dark wounds are healed when a creature finishes a short or a long rest, or when a creature regains hit points.
Each time you hit a creature, that creature gain 1 dark wound stack. A creature can't have more dark wounds than an amount equal to your proficiency bonus. Constructs and undead are can't gain dark wound stacks.
When you hit with a melee attack a creature that is at its maximum amount of stacks, you can consume the stacks, reducing them to 0. When you do so, the creature take additional necrotic damage equal to the amount of stacks consumed.
- Doom Magic
Starting at 3rd level, you are able to harness the power of doom to create magical effects.
Whenever doom magic is used against a target that is at its maximum number of stacks, the target gain 1 dark wound stack after you use the ability.
- Soul Steal. When you hit a creature with a melee weapon attack, you can use soul steal to consume the dark wound stacks, causing additional damage equal to 1d4 necrotic per stack consumed, and regaining the same amount of hit points.
- Soul Crush (7th). When you hit a creature with a melee weapon attack, you can use soul steal to consume the dark wound stacks increasing its power, causing additional damage equal to 1d10 necrotic per stack consumed.
- Void Strike (10th). When you hit a creature with a melee weapon attack, you can use soul steal to consume the dark wound stacks, causing additional damage equal to the difference between your current and maximum number of hit points. The damage is the same as your weapon damage.
- Blood Offering (15th). When you take damage, you can use your reaction to use blood offering. When you do so, your next successful attack causes additional damage equal to the amount taken when you triggered blood offering and stun the target. In addition, for the next minute, all your attacks cause additional damage equal to the amount of stacks the creature had when hit by the attack.
At 7th level, you add your Strength modifier to all your Intimidation checks.
In addition, you gain proficiency with Intimidation, or twice your proficiency if you are already proficient.
At 10th level, you add +2 to all damage rolls with melee weapon attacks.
At 15th level, you gain resistance to bludgeoning, piercing and slashing damage from nonmagical sources.
- Doom Strike
When you reach the 18th level, your critical strikes are infused with the power of doom. When you score a critical hit with a melee weapon attack, you cause additional 100 points of necrotic damage against your target.