Necromantic Shadowplane

Your years of experience in the necromantic energies have granted you the knowledge to open a plane to maintaining control of your thralls. You gain the ability to conjure an extra-dimensional shadowplane with similar effects of Demiplane except the size of the plane is 1000 x 1000 feet that you design the interior of, exactly to your mind's content. You can expend a use of your highest spell slot to increase the size of the plane by a multiplier of two. You cannot create magical objects this way. The dungeon is dim and gloomy, and the atmosphere and air within the shadowplane as you see fit. Additionally, living creatures gain no benefits from sleeping in the shadowplane. You can create A Smith's forge, A Laboratory, and a Plague Doctor's hut among other buildings in this area by will. Any objects that would be taken out of the Shadowplane are immediately dispersed into black mist and vanishes. Any Undead in the shadowplane doesn't fade away and remain under your control so long as they remain within the Shadowplane. If they were to leave the Shadowplane, their control timer resets from that moment of leaving the shadowplane. Additionally, You can also mark off areas where you can open a portal back and forth to the material plane and your shadowplane that lasts for 1 minute, you can do this an equal amount of times to your spell modifier, and regain all uses after a long rest. You must remain concentrated on the portal throughout the whole duration.

You can also make a permanent portal that linked to your Shadowplane to the material plane by expending a spell slot permanently so long as you keep the portal open.