Deserter's Quarters

The trick is in the self-tap clause, and it is the whole reason this exists. The activated ability is hideously expensive: six mana plus the tap to lock down a single creature. But the lock persists only as long as the artifact stays tapped, and the artifact gives you permission to skip its own untap step. So you spend the six once, tap a creature, then deliberately leave the Quarters tapped indefinitely, paying nothing further to keep that creature parked. It is a Pacifism that costs an enormous up-front sum but charges no rent, and one that can be redirected: untap the artifact (by not opting out one turn), and the prisoner is released, freeing you to imprison something else next time. That self-tap permission, common to a small family of artifacts and lands that gate their own untapping, is the structural piece that turns a one-shot activation into a permanent state. The economics are brutal enough that the prison only locks one creature at a time, which is the natural ceiling on a repeatable, no-upkeep removal effect: pay a king's ransom once, hold one threat forever, but only one.