Infernal Shadow Touched

An elf having it's army destroy a town, skeletons and Bone Devils going in and savagely destroying the place as she watches the place burn.

A human hiding in the shadows outside as he has a skeleton brimming with necrotic flame in its chest latch onto a person and explode. And then going up to the survivor and giving them a necrotic slash of their hand, killing them....

Maybe, you struck a bargain with a moving shadow, struck down an innumerable amount of enemies in battle and absorbed their life forces and becoming a conduit, maybe even have Fiendish blood flowing inside of you that allows you certain abilities. With this bloodline, you can raise the dead to fight for you as you rain down Necrotic Hellfire upon your enemies..

Skeleton Summons

Starting at level 1, You begin to practice your dark arts with the most basic of summons. As an action you summon 2 Skeletons from the ground at the cost of 1d4 Hit points, the Skeletons burst forth anywhere within 10 to 60ft of you. They are armed with a shortbow and a shortsword, weapons they had before they died with scraps of armor for protection.

You may use this feature a number of times equal to your proficiency modifier before needing a short or long rest.

Max Skeletons summoned at a time.

Level 1 - 2
Level 6 - 4
Level 12 - 6
Level 16 - 8
Level 20 - 10

 

At 1st level, the summons go away, breaking down into dust after 3 days. At 6th level, you may keep as many as you can summon in one day under your command permanently, but the rest after that break down into dust after 3 days. At 14th level, you may keep the amount of 2 days worth of summoning, the rest breaking down after 7 days. At 18th level, you may keep 4 days worth under your command permanently, the rest breaking down into dust after 14 days. (They can still be "lost" through reaching 0 hp and dying and heal fully from damages as long as they enter a state of rest over a 4 hour period)

A Familiar of Shadow

You get an imp as a familiar. It's bound to you by fate and is eternally loyal. (Use Find Familiar spell for details)

You know this spell as a ritual. It takes one hour to finish and can be done only once per day.

Necromantic Hands

You gain the ability to use Necrotic Slash.

(Use Custom action to make this)

 

Your hand becomes covered in a film of Necrotic energy. Claw at a target within range, causing 1d10+Spell Casting Mod in necrotic damage.

This spell's damage increases by 1d10 when you reach 5th level (2d10), 11th level (3d10), and 17th level (4d10).

Skeletal Explosion

 You gain the ability to cause one of your skeletons to become a necrotic bomb.

(Make it as a Custom Action and keep track.)

Your skeletal minion alights with necrotic fire, bounding towards an enemy within 60ft. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 6d4 necrotic damage on a failed save, or half as much damage on a successful one. You get as many uses as your Spell Casting Modifier.

 

Summon Bone Devils

Starting at level 14, you can bring forth from darkness 2 Bone Devils under your thrall. As an Action you may at the cost of 2d20 hit points summon 2 Bone Devils (1d20 per) as the life force used brings them to your side. You can ONLY summon 2 at a time per Action.

You can use this feature a number of times equal to your Constitution Modifier before needing a Short or Long rest.

At 14th level, you may keep as many as you can make in one day permanently, the rest turning back into black mist that sink into the ground after 4 days. At 18th level, you can keep 2 days worth, the rest turning into black mist after 7 days. (They can still be "lost" through reaching 0 hp and dying. They also heal fully from an 8 hour period of rest.)

Personal Expanded Demiplane

You gain your own demiplane of existence. This area is 40x40 miles, the edges of the area walled in by a thick and impassable fog with the ground going down for 40 miles and the same with the sky, forming a box. This area can be torn from the material plane or created spontaneously. You can open a gate to this personal realm at any time, being 30 feet tall and 20 feet wide with obsidian rock forming the outer edges with only one way in and one way out, the backside having an invisible, nondamaging wall of force repelling people from going through.

The realm starts to shape to your personal desires allowing you to make buildings and structures and has resources you can procure if taken from another plane of existence. This demiplane can be used to store your undead and fiendish soldiers. Plants can grow and animals can live here; the weather is controlled by the one who makes the demiplane.

The gate to and from the demiplane cannot be used to teleport to different areas, just to and from the areas you have opened the gate at. You may leave the gate at an area, leaving it inactive until it turns back on to allow for travel from the area you left from and may only have 1 gate at a time, the previous gate vanishing as if never there.

The summons that stay here can be double of what you have but (So, you could potentially have 3 times the limit placed), you can only have the same limited amount outside of your demiplane. Any extras will be turned to dust or dark mist after the set amount of time and the gate will reject the ones that will disappear after a set amount of time as the demiplane will not allow them entry, and if brought through other means, they will disappear immediately. 

(The gate can not be opened in an area that will not fit it and will be in a transparent state until it has everyone in the area it'd used move out of the way, so it can not be used for an attack, but can be used as a form of transportation for an attack.)