shadow lord

i got the idea from a manga i really enjoyed called solo leveller, vasically the player gets the chance to raise an undead version of the monster slain as his/her minion to be used later.

king of the dead

having been filled with necrotic energy from an evil ritual, at 3rd level you can raise the soul of a dead being you killed or were involved in killing as an undead warrior or mage based on their class before death(does not work on undead), an monster raised just becomes an undead version of that monster.(eg zombie dragon).

you have 3 undead slots and can store 3 different undead units to be summoned later, you can summon or recall any amount of undead units in an action(you can only summon each unit once per short rest),  you have 2 chances per short rest to raise and undead from a killed monster but cannot 4 hours after the monsters death, rolling a critical fail while trying to raise an undead unit means the soul doesnt want to become your unit and immediately disappears, you can only store 1 monster per day, you can exchange used undead slots for another, undead units killed cannot be summoned again and the slot is freed, to raise the monster you have to roll a constitution saving throw beating the challenge rating of the monster + 10 (souls of cr20 or above take up 2 undead slots),1 undead slot is already filled with a dread warrior/spectre ( your choice )that levels up with the player until it ranks up , this cannot be exchanged for another and if killed will be able to be summoned after a long rest. all unit heals per short rest, if you are knocked unconscious or die, your units are immediately recalled.

the shadowy path to glory

your steps are being covered in necrotic energy hiding your tracks.at 7th level,  you have +10ft to your movement speed, you can also choose to turn into a specterish form to levitate 5ft above the ground and pass through walls and have advantage on stealth checks, you cannot perform attacks in this spectre form.

lord of the dead

you have gathered loyal subjects and are more powerful than a measly king. at 10th level, your undead slots have been upgraded to 5 and you now have 3 chances to raise an undead servant per short rest and you can now raise 2 units per day. your original undead unit now gains a rank up into a death knight or a demilich( both should be weaker than their original forms but their strength should be discussed between the player and dungeon master.) depending on the class you picked earlier, their levels also increase as yours does to get closer to their original power.

service to the lord

your undead servants offer up their lives for yours. on your turn, at 15th level, you can use a bonus action to regain hit points equal to 1d10+class level per active undead unit by draining hit points from them. Once you use this feature, you must finish a short rest before you can use it again.

shadow lords retainer

you have become a supreme shadow lord and thus must have a servant of that status to serve you. at 18th level, once per day, on your turn,  you can use up atleast 2(excluding your original unit)  or all of your undead slots releasing your undead units stored in them to transform your original undead unit into a lich for a minute, its power depending on the number of undead slots used. you have to wait a long rest before you can summon your original unit or raise an undead.