This is my first attempt at a homebrew subclass. Trying to balance and give it unique flavor.

The Path of Shadow

Roguish Archetype: SHADOW ASSASSIN

Shifting Shadows: 3rd level

At 3rd level, you gain the ability to form shadows around you to disguise self at will.

Shadow Sight: 3rd level

You become more intune with the shadows. At 3rd level you gain shadow sight. You can see normally in darkness, both magical and non magical, to a distance of 120 feet.

Additionally you can touch another willing creature within 5 ft to apply a shadow mark that appears on them and gifts them Shadow sight for 1 hour. An additional Shadow point can be spent to make the mark and shadow last for 1 hour. It can be gifted in this way to other willing creatures of your choice up to ½ of your Shadow Assassin level rounded down (minimum of 1). The time increases at the 9th level to 6 hours, at 13th level increases to 12 hours, and at 17th hour increases to 24 hours.

You regain all expended shadow sight slots when you finish a short rest. 

Shadow Step: 9th level

The pathways of the shadow realm are open to you the more you become an assassin of the shadow realm. You gain the ability to step from one shadow into another. When you are in dim light or darkness, as a bonus action you can teleport up to 60 feet to an unoccupied space you can see that is also in dim light or darkness. 

You leave shadow decoy in your previous location. The decoy is an illusion that appears to be identical to you, and remains until the end of your next turn. The decoy disappears if it is attacked. A creature making a successful Intelligence (Investigation) check against your DC (8 + proficiency + charisma bonus) will determine that it is an illusion.

Blade of Hunger: 13th Level

You can wield the ceaseless hunger of shadow in your weapons. At 13th level you can imbue a weapon you touch with feasting dark power. For up to 1 hour the weapon is devoid of all light, creating magical darkness in a 5—foot radius and dim light for an additional 10 feet. In addition, weapon attacks made with it deal an extra 2d8 necrotic damage on a hit. As a bonus action on your turn, you can dismiss blade of hunger and cause the weapon to emit a burst of necrotic energy. Each creature of your choice that you can see within 30 feet of you must make a Wisdom saving throw. On a failed save, a creature takes 4d8 necrotic damage, and it is frightened of you for 1 minute. On a successful save, a creature takes half as much damage. At the end of each Of Its turns, a frightened creature can make a Constitution saving throw, ending the effect on itself on a success.

Shadowfell Legion: 17th Level

Starting at 17th level you become a Master of shadows. When you make a killing blow on a creature that cannot see you, they return as a shadow spirit of the shadowfell. The spirit manifests physically in an unoccupied space near their slain body. 

These shadow spirits are semi-incorporeal and exude darkness in a 5 ft radius around them. When summoned in this way roll a 1d4 to determine the emotion it takes on as a part of its form. (Anger, Fear, Despair, Emotionless) The creature is friendly to you and your companions. In combat, the creature shares your initiative count, but it takes its turn immediately after yours. It obeys verbal commands that you issue to it (no action required by you). If you don’t issue any, it takes no action.

The servant can perform simple tasks that a human servant could do, such as fetching things, cleaning, Mending, folding clothes, lighting fires, serving food, and pouring wine. Once you give the Command, the servant performs the task to the best of its ability until it completes the task, then waits for your next Command.

Shadows spirits remain in service to you until they are dismissed by you at will or are reduced to 0 HP. You are limited by the number of Shadow Spirits you can have by your Charisma Modifier. If you create a new Shadow spirit you have a choice to dismiss a spirit of your choice or dismiss the new Shadow Spirit.

Shadow Spirits use the following stat block

Shadow Spirit

I like the idea, but needs refining. Say that you can cast the spell disguise self, because that isn't clear. How many charges do they have? You also need to limit abilities. Maybe amount equal to dex bonus etc. Cause otherwise the lvl 13 ability makes sneak attack combined with it is too powerful. 

In addition to what BramblefootDruid said, that 17th level ability is really weak.

agree with the others that the first ability needs refining.
i dont like the 13th level abilty of your weapon creating 5ft magical darkness, this would mean you were always heavily obscured and so all attacks against your would be at disadvantage for an hour? and your attacks would be at advantage because they are technically blinded in melee with you. seems too powerful.

Any thoughts on if I switch the level 13 ability is switched with the 17th?

Seems like a good idea. Remember to limit this stuff. No limits=abusive play. So limit to proficiency bonus per long rest.

Also, I would like to point out, the 13th level ability is a modified Holy Weapon spell, which clerics get at level 9. I did adjust the language though. 

Blade of Hunger: 13th Level

You can wield the ceaseless hunger of shadow in your weapons. At 13th level you can imbue a weapon you touch with feasting dark power. For up to 1 hour the weapon is devoid of all light, creating magical darkness in a 5—foot radius and dim light for an additional 10 feet. In addition, weapon attacks made with it deal an extra 2d8 necrotic damage on a hit. As a bonus action on your turn, you can dismiss blade of hunger and cause the weapon to emit a burst of necrotic energy. Each creature of your choice that you can see within 30 feet of you must make a Wisdom saving throw. On a failed save, a creature takes 4d8 necrotic damage, and it is frightened of you for 1 minute. On a successful save, a creature takes half as much damage. At the end of each Of Its turns, a frightened creature can make a Constitution saving throw, ending the effect on itself on a success. You may use this feature once before needing a long rest.

I could adjust the magical darkness to non-magical darkness at 5 ft and 10 ft of dimlight?

That seems about right. Otherwise it's a free spell, which not even wizards get (they only get 1,2,3 as spells that they can cast without spell slots, but that's not relevant). Good job. My first homebrew was very bad... That was a year ago, and now I'm making a homebrew class!

I am struggling with how to improve the 17th level ability. I was actually afraid the shadowy servants summoned from a killing blow was OP cause they are just always there, they attack, and have a benefit based on its emotion upon summoning. But it got called weak.

I made this Adjustment on the 17th level ability.

Shadow Strike: 17th Level

Starting at 17th level you become a Master of shadows. When you make a killing blow on a creature that cannot see you, they return as a shadow spirit of the shadowfell. The spirit manifests physically in an unoccupied space near their slain body. 

These shadow spirits are semi-incorporeal and exude darkness in a 5 ft radius around them. When summoned in this way roll a 1d4 to determine the emotion it takes on as a part of its form. (Anger, Fear, Despair, Emotionless) The creature is friendly to you and your companions. In combat, the creature shares your initiative count, but it takes its turn immediately after yours. It obeys commands you can give it mentally that you issue to it (no action required by you). If you don’t issue any, it takes no action.

The servant can perform simple tasks that a human servant could do, such as fetching things, cleaning, Mending, folding clothes, lighting fires, serving food, and pouring wine. Once you give the Command, the servant performs the task to the best of its ability until it completes the task, then waits for your next Command.

Shadows spirits remain in service to you until they are dismissed by you at will or are reduced to 0 HP. You are limited by the number of Shadow Spirits you can have by x2 your Charisma Modifier. If you create a new Shadow spirit you have a choice to dismiss a spirit of your choice or dismiss the new Shadow Spirit.

On a successful attack of the character, any Shadow Spirit within range of your attack target reaches out with a chilling rend and adds their attacks to yours of 2d4 + your charisma modifier cold damage.

Shadow Spirits use the following stat block

(Hopefully you can see the stat block photo)

https://gyazo.com/dbb84f22a1f97e055a486c93e5120a8d

That's good, but remember: you need to say ' when you give a command (no action required, or requires bonus action etc) they perform the task.