Alistair's Create Shadow Lord

This spells creates a Shadow Lord under your permanent command. The Shadow Lord is sentient, and speaks any languages that the shadows that were used to make it knew in life. It also bears the memories of said cratures. The Shadow Lord is loyal to you, and functions as any undead servant, acting on your turn in your bonus action, it also share the same alignment as you, and strives to expand your influence.

You can free the Shadow Lord from your service, and doing so it stops acting on your turn as a bonus action. However, it still remais loyal to you as it's creator, and wishes to work under you to expand your powers, create more shadows and expand your influence.