Build Undead

You can cast this spell only at night. Choose up to six corpses of Medium or Small humanoids within range. Each corpse becomes a ghoul, banshee, ghost, wraith, or  vampire spawn under your control. (The choice is random based on a roll of a d4, respective to the order listed.) (The GM has game statistics for these creatures.)

As a bonus action on each of your turns, you can mentally command any creature you animated with this spell if the creature is within 240 feet of you (if you control multiple creatures, you can command any or all of them at the same time). 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 72 hours, after which it stops obeying any command you have given it. To maintain control of the creature for another 72 hours, you must cast this spell on the creature before the current 72-hour period ends. This use of the spell reasserts your control over up to 12 creatures you have animated with this spell, rather than animating new ones.