Executioner

While some fighters are trained to be delicate dancers with scimitars and whips, others are warriors whose ruthless beliefs are rooted in ideas of conquest, proving and strength: executioners. They are individuals that know that, to make their place in the world, one must claim it, no matter the obstacles in their way, one must crush their enemies and their hopes so their spirit is left as broken as their bodies.

These fighters have a signature brutality that is near impossible to match, and as such, they often find occupations as arena gladiators, mercenary captains, or, simply, as executioners, as the vessel that embodies the ruthless justice that sometimes is required in the world.

Iron Discipline

Beginning when you choose this archetype at 3rd level, your training has instilled in you a rigid sense of survival. When you use your Second Wind feature, you gain resistance to bludgeoning, piercing and slashing damage until the end of your next turn.

Deathblow

Also at 3rd level, you have learnt to execute your foes. Whenever you make a weapon attack against a creature that has completely surrendered (DM's discretion) or a weapon attack of yours reduces a creature to a number of hit points equal to your Execution Threshold, you can immediately reduce them to 0 hit points.

Alternatively, whenever you hit with a weapon attack and it doesn't reduce them to a number of hit points equal to your Execution Threshold, you may choose to deal additional damage equal to twice your Execution Threshold.

Your Execution Threshold equals your Strength modifier + your fighter level. You can use this feature a number of times equal to your proficiency bonus, regaining all expended uses when you finish a long rest.

Blood Sense

At 7th level, as a bonus action on your turn, you can sense weakness around you. Until the end of your next turn, you immediately know the location of any creature with less than half its total hit points within 60 feet of you, and you immediately find out if any creature you can see has any damage vulnerabilities, and what those are. You can use this feature once, regaining the ability to use it again when you finish a short or long rest.

Cruel Repute

Starting at 10th level, you have learnt to instill fear in the hearts of your enemies. When you use your Deathblow, Iron Discipline or Blood Sense features, choose any number of creatures within 30 feet that can see you. Those creatures make a Wisdom saving throw (DC = your Execution Threshold) or become frightened of you until the end of your next turn.

Improved Iron Discipline

At 15th level, whenever you use your Iron Discipline feature, you can also either gain resistance to all damage until the end of your next turn, or gain temporary hit points equal to your fighter (choose one each time).

Additionally, you also gain the benefits of your Iron Discipline feature your Action Surge feature.

Death Dealer

By the time you've reached 18th level, you have become the ultimate executioner. Creatures frightened by you have their speed reduced to 0, and when you use your Deathblow feature on a creature frightened of you, it doesn't expend a use.