Gravedigger

 Folks in the outskirts talk of the gravediggers, ones that walk among the paths less travelled and abandoned battlefields, burying bodies of those who no one bothered to check on, the bad tounges speak of bones stolen, of amalgams of bodies walking among these people, all tales of course, besides...

 It's not like the corpses were using them anymore. 

Lurcen Billows, Gravedigger.

Level 3: Approaching of the grave

You can call on the forces of death to pull your prey ever closer to it. While a creature is marked by your Hunter’s Mark, the extra damage dealt by the spell is necrotic damage, when a marked creature recieves radiant damage deal an extra d12 necrotic damage, but the effect ends, you can spend a bonus action to reactivate this effect during your turn a number of times equal to your proficiency modifier.

You also Add the following to your spells without them counting for your learned spells:

Level 3: Spare the dying, Toll the dead, False Life, Inflict wounds

Level 5: Gentle repose

Level 9: Speak with dead, Vampiric touch

Level 18: Contagion, Reincarnate

Level 3: Grave decisions

You gain one of the following feature options of your choice. Whenever you finish a Short or Long Rest, you can replace the chosen option with the other one.

Grave maker

Once per turn, when dealing necrotic damage give that ammount of temporary hit points to a creature of your choosing withing 30ft of yourself.

Grave robber

Your thirst for death brings your enemies closer to it. When you hit a creature and deal necrotic damage make the next attack roll towards that creature be with advantage. You can apply this effect only once per turn.

Level 7: Shambling companion

You always have the spell Summon Undead always prepared and it doesnt count against your learned list of spells, once per long rest you can cast this spell with a spell level equal to your proficiency modifier without expending spellslots or material components, when it is summoned if you had Hunter's Mark active the summoned undead holds concentration instead of you, all efects that would normally apply to your Hunter's Mark also apply to the summoned undead. 

Level 11: Push to the grave

The reactivation of Hunter’s Mark  can be done with an attack instead of a bonus action as long as you hold concentration.

Level 15: Advanced companion

When your summoned undead dies activate the extra damage from approaching to the grave, if the mark is not active activate it as a free action.