Duelist

Maybe you're a noble and dueling is part of your culture or maybe you do it for the adrenaline rush. Regardless of why you have trained yourself to excel in duels and defeat your opponent. 

Challenge Declaration

When you choose this archetype at 3rd level, you learn how honorably declare a challenge in combat. This not only is needed as set up for your Duelist abilities but also grants favorable passives. You can only declare challenge on a single creature at a time, you cannot challenge another creature until the challenged creature has either died, been knocked unconscious, or fled combat. You may only declare a challenge if you are wearing either light or no armor and are not using a shield. 

Honorable Duel: Duels are sacred and others shouldn't interrupt, once you declare a challenge on a creature you may add your charisma modifier to your AC for attacks from other creatures. 

Professional Duelist: While attacking a challenged creature with a weapon you are proficient with you can add an extra half your proficiency bonus (rounded down) to the attack rolls. 

Cowards Punishment: If the creature flees combat then next time you see it you can declare challenge as a free action and the creature has to make a Wisdom saving throw or take Psychic damage equal to a number of d6's equal to your proficiency bonus. The save DC for this is 10 + your proficiency bonus.

Professional Duelist

Starting at 3rd level, you gain the Dueling fighting style from the fighter class. 

You gain the ability to set up feints against creatures that you have declared challenge on. When you hit a challenged creature with a melee attack you can spend either your bonus action or reaction to gain advantage on the next attack against this creature. Every time after the first time you do this it has a chance to fail, this is decided by an insight check by the challenged creature. The DC of this check is 18 + your DEX modifier, however every time the challenged creature fails this check the base DC is decreased by 2. (I.e. 1 failure = 16 + DEX, 2 failures is 14 + DEX etc.) The base DC can decrease to a minimum of 6.   

Duelist Equipment Training

.At the 9th level, you have trained yourself to duel against and with many different weapons. All weapons that don't have the heavy property now count as Finesse weapons for you. 

You have learned to use your armor or lack of it to its fullest potential. While wearing light armor you can add half your proficiency bonus to your AC. While wearing no armor you add your DEX modifier twice to your base AC instead of just once.  

Your Dueling fighting style now gives you extra damage equal to your proficiency bonus instead of +2. 

Finishing Blow

Starting at 13th level, when you reduce a creature to zero hit points you can decide how to finish it granting you favorable bonuses. (Basic ruling for knocking creatures unconscious can still trigger these effects)

Brutal Execution: You brutally put down your enemy, all creatures within a 10 ft. radius must make a DC 15 wisdom saving throw or become frightened of you. 

Elegant Finisher: You elegantly put your enemy to rest, you gain temporary hit points equal to your proficiency bonus. 

Mercy: You attack deals nonlethal damage, your act of mercy makes other creatures hesitant to attack you. All creatures with an INT of 6 or higher who witness this have disadvantage on attacks against you until you kill a creature in their presences. 

(Optional Mercy Killing, if the creature is in immense pain, cannot be saved from some kind of mind control, is diseased and changed forcibly, or is a non-sentient undead then you can gain the benefits of mercy while still dealing lethal damage.)

Duelist Burst

At the 17th level you have learned to burst out with energy to end your duel as fast as possible, in this state you feel like you could kill an army.  

As an action you activate your Duelist burst. For the next minute you gain several benefits and effects. 

I Can Take You All On!: Your challenge declaration now affects all creatures within 10ft. of the initial target. 

Adrenaline Rush: You gain haste. 

Maximum Effort: When you deal non sneak attack damage the size of your damage die is increased by 1. (A 1d12 weapon is instead increased to 2d8)

When this ability ends you become stunned for 1d4 rounds and gain 1 exhaustion point. 

You can use this ability twice per long rest.