Combine undead

This spell creates an greater undead servant. Choose up to 10 skeletons or zombies in the casters control.  Your spell imbues the target with a foul mimicry of life, twisting its form and raising a greater undead creature. The target becomes a undead creature of cr lvl to 1/2 of the total cr used(10cr 1/2 means 1 cr undead up to cr 5)

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 60 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.

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 four creatures you have animated with this spell, rather than animating a new one.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, you combine or reassert control over two additional undead creatures for each slot level above 5th.  At 9th level you can combine all undead in your command to create a temporary "legendary" undead creature that last for 5 turns. (Thinking like a lich or something?)