Concentrated masters of the blade that are united under the mantra of finding the power to take control of their own lives, the Darkslayers are a loose order of a school of swordsmanship that practices patience, speed and precision, while not slacking on the power to see their enemies through. By practicing deep meditation and awakening the deepest recesses of their minds, they come to those in need of extraordinary power, whether selfish or selfless, who then become students of the Darkslayer school. Grueling and unyielding, Darkslayers typically leaves slews of corpses in their path to take back control of their lives, and once they have succeeded, dedicate their lives to upholding said power and passing off their knowledge to newer students, thusly ensuring that the technique will never die.

Rising Concentration

Starting when you choose this archetype at 3rd level, you grow in power the more you fight flawlessly with no hesitation. Every step you take and every move you make has an influence on your Concentration, which is measured in levels. At 3rd Level, you have a maximum of two levels of Concentration, which increase to 3 at 5th level, 4 at 7th, 5 at 9th, 6 at 11th, 7 at 13th, 8 at 15th, 9 at 17th and 10 at 19th level. At the end of every combat, your Concentration is reset to zero. Your level of Concentration increases by 1 when you make the attack action and hit, by 1 for every time an attack misses you, by 1 for every Dexterity saving throw you succeed and by 2 if you end your turn not having moved. Your Level of Concentration decreases by 1 for every attack you miss during your turn, by 1 for every attack that hits you, by 1 for every saving throw you fail and by 1 for every 5 ft. you move that is not towards a hostile creature. 

For every level of Concentration you have, you have a +1 bonus to damage rolls on creatures that you hit, for a total maximum of a +10 damage bonus at Concentration Level 10.

Upon reaching Concentration Level 5, your readiness towards threats that approach gives your mind the ability to shrug off lesser mind-altering effects. When at this Concentration Level, you have advantage on saving throws against being charmed and frightened, and you have proficiency in Wisdom Saving Throws.

Starting at Concentration Level 9, your absolute focus becomes so all-encompassing that you gain the ability to identify multiple incoming threats seemingly at once. While at this Concentration Level, you gain an additional reaction each round. When you've reached Concentration Level 10, this is increased to 2 additional reactions instead.

Saving Throws. Some of the features that your Concentration allows access to require your targets to make a saving throw to resist its effects. The saving throw DC is calculated as follows:

   Concentration save DC = 8 + your proficiency bonus + your Wisdom modifier

Unparalled Skill

Upon choosing this archetype at 3rd level, you can use either your Dexterity or Strength modifier when making attacks with a weapon that deals slashing damage. Additionally, your concentration allows you to have a degree of foresight when unencumbered by armor. Your armor class when not wearing armor and not wielding a shield equals 10 + your Dexterity modifier + your Wisdom modifier.

Additionally, when you reach Concentration Level 3 or higher, you can use your reaction to parry an attack against you with a held weapon, adding your proficiency bonus to your AC for that attack.

Furthermore, when you reach Concentration Level 7, Your attacks become critical on rolls 19 or 20. When you reach Concentration Level 10, your attacks become critical on rolls of 18-20 instead.

Spirit Summoning

Starting at Concentration Level 1, your immaculate concentration manifests in a mass of spiritual blades that you can summon at will. These blades are considered magical, dealing 1d6 + your wisdom modifier as piercing damage to any creature they hit, and have a range of 90 ft. You can replace any attack that you make during your attack action with one of these blades, that have an attack bonus equal to your proficiency bonus + your wisdom modifier. For every 3rd Concentration Level that you have, these blades gain an additional +1 bonus to hit (for a max. bonus of +3 at Concentration Level 9).

Your battle focus affects your prowess with your Spirit Blades, increasing in versatility the more concentrated you become, manifesting in different uses for them. By default, this allows you to exhibit fine control using one. You gain the mage hand cantrip, and whenever you cast it, it manifests as one of your spirit blades.

When you reach Concentration Level 4, this gives you the ability to concentrate your essence on a single spirit blade you fire, and using it to perform a Spirit Stride. As part of an attack when you hit a creature, you can choose to travel along with the blade. When it hits a creature or an object, you then teleport alongside the blade and appear at a space adjacent to the target hit.

At Concentration Level 6, this gives you the ability to focus your attention a myriad of different attacks at once, allowing you to fire a Blistering Impact. As an action, you can summon 8 spirit blades at once and fire them all at once, either at the same or different targets. These blades each deal the damage of one of your spirit blades.

Finally, when you reach Concentration Level 8, this gives you the ability to shower an area in a torrent of spirit blades, giving you the ability to summon a Hail of Blades. You shower the area in a 20 ft. cube with a hail of blades, forcing all creatures within to make a Dexterity saving throw. On a failed save, the creatures take 8d8 piercing damage and have their speed halved until the end of their next turn.

Regardless of how many times you reach the necessary Concentration Level to summon these spirit blade forms, you can use any of these techniques an amount of times equal to your Wisdom modifier, and you can't use them again until you have finished a long rest.

Quickdraw Cut

When you reach 7th level, you gain the skills to make blade attacks quicker than the eye can see, using your spiritual powers to cut through space itself. After you hit a creature on your turn, you can immediately use your bonus action to make an additional special attack. When making this attack, you can choose a spot within 60 feet of you. You then slash in a 5 ft. cube centered on that spot. Creatures in the area must make a Dexterity saving throw, or take 1d8 + your Dexterity modifier + your Wisdom modifier as slashing damage.

Starting when you reach Concentration Level 6, you can take your reaction to immediately after a successful Quickdraw Cut to make a follow-up cut with the same effects, either on the same or a different creature. If you target a creature that you hit the creature with the first cut, it has disadvantage on the second saving throw.

Any additional reactions granted to you by reaching Concentration Level 9 or above can be used to make this attack continuously, as long as you keep hitting a creature with it.

Doppelgänger

Upon reaching 10th level, your spiritual focus becomes so great that it can manifest as a seperate entity that acts alongside you. As a bonus action, you can manifest a doppelgänger. When doing so the form is tethered to you. The doppelgänger has the appearance of a radiant white, almost translucent form that otherwise have your physical features. These forms have 1 hit point, an AC of 12 plus your proficiency bonus, have your saving throw bonuses and are immune to all conditions. The doppelgänger remains for 1 minute.

The form remains in your space and acts as a perfect mirror to your actions. While the doppelgänger remains active, you can add an additional damage die to whatever weapon you are currently wielding. When you've reached Concentration Level 5 or above, the doppelgänger also allows you to add your Wisdom modifier to damage you deal.

If you've reached Concentration Level 5 or higher while your doppelgänger is active, you can use a bonus action to draw the active doppelgänger back into yourself, equivalent of casting the haste on yourself. This casting of the spell does not require concentration, but if you drop below Concentration Level 5 while it is active, the spell immediately ends and you become stunned until the end of your next turn.

You can use this feature once, after which you can't use it again until you've finished a short or long rest.

Perfect Appraisal

Starting at 15th level, your technique in for knowing the creatures the interact with becomes ever stronger, and you gain the ability to study them to find their weakness. As an action, you can begin studying a creature's movements, parades and general actions for a minute, trying to find the best way to slip past their guard. Once 1 minute has passed of uninterrupted study, you can make an insight check contested by the creature's deception check. If you succeed this contest, the next time you hit the creature with an attack or spell within the next minute, the creature has vulnerability to all damage dealt by the attack, and the effect ends. Alternatively, you can use this to gain advantage on Charisma checks against the chosen creature for 1 minute. Once a target has been succesfully affected by this feature, it can't be affected by it again until 7 days have passed.

When you reach Concentration Level 4, The first time you land a critical hit on a creature you're currently studying or have studied within the last minute, you regain a use of your Spirit Summoning Techniques as you siphon a bit of their spiritual power.

If you have reached Concentration Level 8, you can instead make the insight check immediately as an action.

Twilight Pinnacle

At 18th level, you have reached the pinnacle of bladesmanship, allowing you to attack and move in ways that only very few can claim to. While you are unarmored and not wielding a shield, your walking speed increases by 10 feet, and you infused your dashes with the spiritual power at your control. When you take the dash action, you can move through other creatures as long as you end up on a space next to them.

When you reach Concentration Level 4, You gain the ability to make a single weapon attack when taking the dash action as well. Finally, when reaching Concentration Level 6 and you dash, you gain the ability to take half damage on failed Dexterity saving throws, and take no damage when succeeding a Dexterity saving throw until the beginning of your next turn.

Additionally, once you have reached Concentration Level 8, you can choose to re-roll a single attack roll you make during each of your turns. You must use the new roll.

End of All

Upon reaching 18th level, your utilization of your surroundings, bladesmanship and concentration allow you to reach the pinnacle of what a mortal fighter can reach, using your weaponry and spiritual power to shake the foundations of reality.

When you reach Concentration Level 7, you can replace one of the attacks in your Attack action to instead target a 30-foot cone directly in front of you, using your spiritual powers to cleave the air in the area and force creatures in the area must make a Dexterity saving throw. On a failed save, the creatures take 3d10 force damage and are slowed down as if affected by the Slow for 1 minute. Once you have done this attack, you can't do so again until you have finished a short or long rest.

Additionally, you can choose to give up your entire Concentration Gauge to unleash a strike quicker than the eye could hope to track, slashing and tearing at The Weave itself within 30 feet of you. All creatures within this area must make a Dexterity saving throw. On a failed save, the creatures take 4d6 times your current Concentration Level as resistance-ignoring slashing damage, up to a total of 40d6 slashing damage at Concentration Level 10. Once you have used this feature, you gain temporary hit points equal to twice the Concentration Levels consumed, you are unable to refill your Concentration Gauge for 2d4 turns and you can't make the action again until you have finished a long rest.