Seal Away

You prepare a magical prison, trapping a creature you can see within range for eternity. The target must succeed on a Wisdom saving throw or be imprisoned. On a success, it is immune to this spell for 1 year. While imprisoned in this way, the target does not age, does not need to eat, breathe, or drink, and cannot be found by any divination magic. You select the form of the prison when you cast the spell. Common options would be a sealed demiplane, miniaturized within a gemstone, or trapped in a cavity deep below the ground.

When you cast the spell, you must specify the condition by which the target can be freed. The condition can be as elaborate or as specific as you desire, but it must be reasonable and possible (your GM must approve the condition). The condition can involve a creature’s name, identity, or characteristics, but not game concepts such as level, class, or hit points. Dispel magic cannot free the target. If the condition comes to pass, the target is instantly freed.