The Dark Slayer is a warrior of intense focus, wielding a unique mix of martial prowess intertwined with magical ability.  They pride themselves on speed and precision, cutting down their foes in a blur of lights and slashes as they blink about on the battlefield.

Focus

Beginning when you choose this archetype at 3rd level, you can generate magical energy that is tied to your concentration in battle.  This energy is represented by a number of focus points equal to your Wisdom modifier (Minimum of 0) + your Proficiency Bonus.  Having these focus points grants you special bonuses while in focused concentration and you can expend it to power special techniques called focus strikes.  You regain all expended focus points when you finish a long or short rest.

• Focused Concentration - As a Bonus Action, you can expend 1 Focus Point to enter a state of hyper awareness and you begin concentrating, as if concentrating on a spell.  This state lasts for 1 minute and it ends early if your concentration is broken or if you end your turn with 0 Focus Points.  While in this state you deal extra force damage the first time you hit a target with an attack on a turn.  The extra force damage is equal to 1 for every 2 focus points you have.  You can also regain expended focus points or lose focus points while in this state.  You regain 1 expended focus point  if you take the Attack action and at least half of your attacks hit targets hostile to you (Rounded Up), if you land a critical hit against a target hostile to you, or if you reduce a creature hostile to you to 0 hit poinnts with an attack.  Conversely, you lose 1 focus point if you roll a 1 on the d20 when you make an attack roll, or if you lose concentration as a result of taking damage.  You can gain or lose 1 focus point only once per turn reach while in this state.
• Focus Strikes - At 3rd level, you automatically learn three focus strikes, which are special techniques powered by your focus points.  You learn additional focus strikes when you reach 7th, 10th, and 15th level in this class.  You can only use a Focus Strike once per attack.
• Saving Throws - Some focus strikes may require your target to make a saving throw to resist its effects.  The saving throw DC is calculated as follows:  Focus Save DC = 8 + your Proficiency Bonus + your Wisdom Modifier

Focus Points

Beginning when you choose this archetype at 3rd level, you can generate magical energy that is tied to your concentration in battle.  This energy is represented by a number of focus points equal to your Wisdom modifier (Minimum of 0) + your Proficiency Bonus.  Having these focus points grants you special bonuses while in focused concentration and you can expend it to power special techniques called focus strikes.  You regain all expended focus points when you finish a long or short rest.

Focus Strikes

Your focus points can be used to fuel certain abilities.  At 3rd level, you learn the following Focus Strikes.

• Charged Strike - When you hit a target with an unarmed strike, you can expend 1 focus point to deal an additional 1d6 force damage.  If you are in focused concentration, the extra force damage becomes 1d8 instead.  This focus strike has additional effects when you hit with your unarmed strike depending on the number of additonal focus points expended.  When you spend 2 focus points, the target must make a Strength saving throw, or be pushed 10 feet away from you, or be lifted 10 feet off the ground (your choice).  With 3 focus points the target is also knocked prone on a failed save.  If the target is a Huge or larger creature, it automatically succeeds on the save.
• Judgement Cut - As a bonus action immediately after taking the attack action, you can spend 2 focus points to make rapid slashes that travel to a point you can see within 15 feet of you.  Each creature within 5 feet of the point must make a dexterity saving throw, taking 2d6 slashing damage on a failed save, or half as much on a successful one.  This damage becomes 2d8 if you are in focused concentration.  You must be wielding a melee weapon that deals slashing damage in order to use this focus strike.
• Trick - As a bonus action, you can expend 1 focus point to teleport to any unoccupied space you can see within 10 feet of you.  This increases to 15 feet if you are in focused concentration.

Mirage Blades

Also at 3rd level, you can conjure spectral blades that fly towards your enemies.  You gain a new attack option that you can use with the attack option.  This special attack is a ranged spell attack with a range of 30 feet.  You are proficient with it, and you add your wisdom modifier to its attack and damage rolls.  Its damage is Force, and its damage die is a d6.  This special attack can be used for any of the attacks you make as part of the Attack action.

Bonus Proficiency

At 7th level, you gain proficiency in the Insight or Perception skill (Your Choice).  If you are already proficient in both skills, you instead gain proficiency in one skill of your choice.

Additional Focus Strikes

Also at 7th level, you learn two additional focus strikes, which you can choose from the following options.

• Focused Blade - When you make an attack with a mirage blade, you can expend 1 focus point to increase its range to 60 feet and deal an additional 1d6 force damage on a hit (for a total of 2d6 force damage.)
• Lunar Phase - When you make an unarmed strike, you can expend 2 focus points to lunge forward 10 feet toward the target with a vicious spin.  This movement does not provoke opportunity attacks and deals an extra 1d6 force damage on a hit.  If you are in focused concentration and the attack hits, the target must make a strength saving throw, or be knocked prone.  If the target is Huge or larger, it automatically succeeds on the save.
• Rapid Slash - When you use trick or any similar such spell or ability (such as the Misty Step spell), to teleport to an unoccupied space within 5 feet of a target you can see, you can use your reaction to expend 1 additional focus point to make one melee weapon attack against that target.  You must be wielding a melee weapon that does not have the two-handed or heavy property in order to use this focus strike.
• Stinger  - As one of your attacks when you take the Attack Action, you can spend 2 focus points and lunge forward in a straight line up to 15 feet towards a target.  On a hit you deal an additional 1d6 force damage.  If you are in focused concentration, you deal an additional 2 force damage for every 5 feet of distance you traveled before making the attack.  You must be wielding a melee weapon that deals slashing or piercing damage in order to use this focus strike.

Calm Focus

Beginning at 10th level, you regain 1 expended focus point when you use your Second Wind feature.

Further Additional Focus Strikes

At 10th level, you learn two additional focus strikes.  Your choice can be from any of the options you didn't take at 7th level, or you can choose from the following options.  You can also replace one focus strike you took from 7th level and replace it with one you didn't take at 7th level or with another from the following options.

• Kick 13 - As a bonus action immediately after taking the Attack Action and using Unarmed Strikes for your attack, you can expend 3 focus points and make one additional unarmed strike.  If you are in focused concentration, you make one more additional unarmed strike as part of the same bonus action.
• Overdrive - When you take the Attack action, you spend 3 focus points and replace one of your attack with a wave of energy you release from your weapon in a 15-foot straight line that is 5 feet wide.  Each creature within this line must make a Dexterity saving throw, taking 3d6 force damage on a failed save.  If you are in focused concentration you can replace two attacks instead of one.   This focus strike has additional effects depending on the number of addtional focus points expended.  With 4 focus points, each Large or smaller target who fails the save is pushed 5 feet away from you and is knocked prone.  With 5 focus points the force damage becomes 3d8.  The weapon you are wielding must not have the two-handed property in order to use this focus strike.
• Spiral Blades - As a bonus action, you expend 3 focus points and manifest several mirage blades that spin around you until the start of your next turn.  During this time, whenever a creature starts its turn within 5 feet of you or enters that area for the first time in a turn, it takes 1d6 force damage.  If you are in focused concentration the force damage becomes 1d8.
• Void Slash - When you take the Attack action, you can expend 3 focus points and replace one of your attacks with a wide strike that radiates energy in a 15-foot cone.  Each creature on the ground within that area must make a Dexterity saving throw.  A creature that failed the save takes 3d8 force damage plus your weapon damage, and is pulled 5 feet towards you.  On a successful save, a target takes half as much damage and isn't moved.  If you are in focused concentration, a target that failed the save is also knocked prone.  The weapon you are wielding must not have the two-handed property in order to use this focus strike.

A Little Motivated

Beginning at 15th level, whenever you roll a Dexterity or Wisdom saving throw while in a focused concentration, you can use your reaction to expend at least 2 focus points to add half the number of expended focus points to the save.

Motivated Focus Strikes

At 15th levle, you learn two additonal focus strikes.  Your choice can be from any of the options you didn't take at 7th or 10th level, or you can choose from the following options.  You can also replace one Focus Strike that you took from 7th or 10th level, and replace it with one you didn't take at those levels, or with another from the following options.

• Heavy Rain Blades - When you hit a creature with your Mirage Blade attack, you can expend 3 focus points to deal an additional 2d4 force damage, as several blades follow suit.  if you are in focused concentration, you deal 2d6 force damage instead.  The target must then make a Strength saving throw, or become restrained until the start of your next turn.  if the target is restrained while in midair, it remains suspended there until the start of your next turn.
• Hell on Earth - You slam your fist into the ground and release a powerful burst of energy.  As an action while in focused concentration, you expend 5 focus points to cast the Destructive Wave spell.  When you cast the spell in this way, you deal force damage instead of the spell's two damage types.  You can use this focus strike once, and must finish a long rest in order to do so again.
• Judgement Cut End - You slash at blinding speeds, as if appearing in several places at once.  As an action while in focused concentration you expend 5 focus points to cast the Steel Wind Strike spell.  When you cast the spell this way, you make melee weapon attacks instead of spell melee attacks.  You must be wielding a melee weapon that deals slashing damage in order to use this focus strike.  You can use this focus strike once and must finish a long rest in order to do so again.
• Trick Ddoge - Your focus allows you to teleport out of harm's way.  When you are targeted by an attack, you can use your reaction to expend 4 focus points and teleport to any unoccupied space you see within 15 feet of you.  If you are in focused concentration you can choose to forego expending focus points and instead make a Wisdom (Insight) check against the attacking creaeture's attack roll.  On a successful check, you spend no focus points and instead gain 1 focus poinnt as you teleport away at the very last moment.  On a failed check, the teleport fails and the attack automatically hits you.
  Alternatively, when you are subjected to an effect that allwos you to make a Dexterity saving throw to take only half damage, you can use your reaction to expend 3 focus points and instead take no damage if you succeed on the saving throw, and only half damage if you fail.  On a success or a fail, you teleport to any unoccupied space you can see within 15 feet of you.

Doppelganger

At 18th level, you can use an action while in focused concentration to conjure a spectral clone of yourself in an unoccupied space within 10 feet of you.  The clone lasts for 1 minute, and ends early if your focused concentration ends, or as a bonus action on your turn.  The clone is illusory and magical in nature.

In combat, it shares your initiative count, but it takes its turn immediately after yours.  It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take another action.  That action can be the Attack, Dash, Disengage, or Dodge.  For its reaction, it can only do an opportunity attack.  

When it takes the Attack action, it makes two weapon attacks with a spectral melee weapon that deals 1d8 force damage, and uses your bonuses for its attack and damage rolls.  You can also command the clone to use Focus Strikes as part of its attacks (no additional action required), expending your focus points when it does so.  

You can summon your clone once, and must finish a long rest in order to do so again.