Bind Undeath

This spell creates an undead servant by conjoining the necromantic energies of other undead. Choose any number of skeletons, zombies, or other undead under your control within range, all but one of these are destroyed in the casting of this spell. Effectively you conjoin their challenge ratings to summon one creature of that challenge rating. Your spell imbues one of the targets with a more potent mimicry of life, raising it as an undead creature. The potency of this creature is determined by the spell slot you use to cast this spell. A 3rd level spell slot can summon up to two CR 1/2 or one CR 1 undead. A 4th level slot can summon up to two CR 1 or one CR 2 undead, etc. At the DM's discretion, a body must be carefully selected or prepared to house such powerful magics. To avoid such a complication a spellcaster may acquire a specially prepared black onyx as a focus for this spell.

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 90 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). If the creature can speak it can mentally contact you as well. 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've given it. To maintain control of the creature for another 24 hours, you must cast this spell on the creature again before the current 24-hour period ends. This use of the spell reasserts your control over up to a combined CR of 1 instead of animating a new creature. This method of control scales with spell level as well, with a 4th level slot reasserting control up to a combined CR of 2, etc.

Keep in mind creatures reanimated by an undead's effect, such as a Shadow or a Husk Zombie, are not under the control of the spellcaster.  In the case of a Wight or Wraiths effect, however; creatures reanimated in this way count towards the total challenge rating of a wight or wraith for the purposes of reasserting control.