Tim-Tim's Kindred Keep

This spell allows undead creatures under your control to occupy any particular area of your choice. The area around you when you cast the spell becomes suffused with necromantic magic. The spell otherwise has no effect until the 10th and final casting.

If you cast Tim-Tim's Kindred Keep in the same area for 10 days the spell takes effect. By placing the onyx used as as the material component for this spell you can have a number of undead creatures up to your proficiency bonus bound to the chosen area. While bound in this way they do not count against your number of undead under your control, but they cannot willingly move more than 500 feet away from the onyx. If they are ever more than 500 feet away they take the shortest and most direct route back to the onyx. While you are within 5 feet of the onyx, as an action you can change which undead creatures are bound to the onyx. 

If you cast this spell again, the previous instance of the spell ends. The spell also ends if you move the onyx more than 500 feet away from where it was originally placed, if a spell or effect such as dispel magic is cast on the onyx, or if the onyx enter the area of an spell or effect such as antimagic field.