Curseblade Fighter

Those who use this archetype give themselves into a dark force for power, letting themselves be taken in by a curse
To be a Curseblade is a risk, one that can't be taken too lightly, and one that may alienate others around them

Cursed Frenzy

When you are reduced to 0 HP by any damage source, you enter an uncontrollable blood frenzy and gain temporary HP equal to 5 times your level.
During this frenzy, you can take death saving throws as normal, returning to consciousness if you succeed. Without an apparent foe in sight, you will attack the nearest living creature. Should you run out of temporary hit points, or succeed your death saving throws, this frenzy is dispelled, and all temporary hit points are removed
If you reduce an enemy to 0 hit points while in this state, you also regain consciousness and hit points equal to your hit dice

Curse of Pride

Starting at 7th level, your critical strikes lay a Cursemark on the target. This Cursemark remains until dispelled by any spell that dispels magic or curses or a restoration spell, as well as if the Cursemarked target lands a critical hit on you or an ally

When you make a successful attack action against a creature marked with the curse, the damage dealt also reduces the creature's max hit points by your Fighter level times two, or half the damage dealt, whichever is lower
This effect is removed if the Cursemark is dispelled, returning the maximum hitpoints to their original state

Additional Fighting Style

At 10th level, you can choose a second option from the Fighting Style class feature.

Archery

You gain a +2 bonus to attack rolls you make with ranged weapons.

Defense

While you are wearing armor, you gain a +1 bonus to AC.

Dueling

When you are wielding a melee weapon in one hand and no other weapons, you gain a +2 bonus to damage rolls with that weapon.

Great Weapon Fighting

When you roll a 1 or 2 on a damage die for an attack you make with a melee weapon that you are wielding with two hands, you can reroll the die and must use the new roll, even if the new roll is a 1 or a 2. The weapon must have the two-handed or versatile property for you to gain this benefit.

Protection

When a creature you can see attacks a target other than you that is within 5 feet of you, you can use your reaction to impose disadvantage on the attack roll. You must be wielding a shield.

Two-Weapon Fighting

When you engage in two-weapon fighting, you can add your ability modifier to the damage of the second attack.

Curse of Greed

Starting at 15th level, after your weapon attacks score a critical hit, any weapon attacks made on your next turn have a critical range of 15-20 instead.
If a critical hit is landed again and a Cursemark has been applied, the Cursemark now gives the targeted creature a disadvantage on all attack rolls made against the Curseblade.

Curse of Blasphemy

At 18th level, you have mastered your curse and made it your own. Upon dealing damage to an enemy with a Cursemark applied, you regain hit points equal to 2 + your Constitution modifier. You don’t gain this benefit if you have 0 hit points or have already entered your Cursed Frenzy.