Create Spectral Servant

You can only cast this spell at night. When you cast this spell, choose a humanoid within range. The humanoid must have less than 10 hit points to be targeted, otherwise the spell fails. This humanoid must make a Charisma saving throw; they roll with disadvantage if they would make a death saving throw on their next turn. On a failure, the target's soul is ripped from their body and becomes a ghost. 

As a bonus action on each of your turns, you can mentally command this creature. 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. The creature is under your control for 24 hours, after which it stops obeying any command you have given it. To maintain control of the creature for another 24 hours, you must cast this spell on the creature before the current 24-hour period ends. The same amulet must be used every time the spell is used to maintain control over the same ghost.