Undead Servant

This spell can only be cast at night. This spell creates an undead servant. Choose a pile of bones or a corpse of a Large or smaller creature within range. Your spell imbues the target with a foul mimicry of life, raising it as an undead creature. The DM will have the game statistics for raised undead. If the target is Large or not humanoid, it can only be raised as a zombie or skeleton of it's type. If the target is a Medium or smaller humanoid, you may choose to raise it as one of the following types of undead if you have the necessary components (you cannot use a spellcasting focus to replace these components):

Ghoul: A snake's fang; a black gem worth at least 100 gp, which this spell consumes

Ghast: a piece of rotting flesh or a petrified tongue; a black gem worth at least 300 gp, which this spell consumes

The creature is under you command for as long as you are on the same plane of existence. On each of your turns, you can use a bonus action to mentally command any creature you made with this spell if the creature is within 300 feet of you (if you control multiple creatures, you can command any or all of them at the same time, issuing the same command to each one). You decide what action the creature will take and where it will move during its next turn, or you can issue a general command, such as to guard a particular chamber or corridor. If you issue no commands, the creature only defends itself against hostile creatures. Once given an order, the creature continues to follow it until its task is complete, at which time it will wander and attack any living beings in the area until you issue another command. If the creature becomes an intelligent undead, it will act as it believes you would want it to do. 

Creating an undead that will eternally serve you is very taxing. You are unable to regain hitpoints until you finish a long rest and you gain one level of Exhaustion. You can only cast this spell once every week and can only have 5 undead at a time under your control through this spell.