Tomb of the Lich God (Revised)

You banish a target that you can see within range into a reeking, somewhat labyrinthine, foggy, 190 foot by 195 foot demiplane that is inhabited by 2d6 crawling claws, 1d10 shadows, 2d8 zombies, 2d6 + 1 ghouls, 1d8 ghasts, and 1 cambion that has the undead subtype and the mage spell list. The lair is also mostly (75%) covered in fog. The fog spreads around corners and its area is somewhat obscured. The target remains there for the duration or until it escapes the lair.

The target can use its action to attempt to escape. When it does so, it makes a DC 23 Intelligence check. If it succeeds, it escapes, and the spell ends (a lich or dracolich automatically succeeds). Any undead remaining in the lair after the target escapes that have not taken any damage from the target, instantly vanish from existence. However, any undead that remain in the lair that have been damaged by the target comes to the material plane in the same state it was before the lair dispersed.