Spectral Prison

Tap-down auras live or die on how the opponent breaks the lock, and this one writes its own escape hatch into the rules text. The lock only bites once the creature is already tapped, since the aura stops the untap step rather than tapping anything itself; cast on an attacker that has already swung, it strands that creature sideways indefinitely, contributing no blocks and no future attacks. But the second clause turns the prison into a fragile leash. Any spell that targets the enchanted creature, including the controller's own pump spell or a self-bounce, sacrifices the aura and frees the prisoner. That makes the effect porous in a way hard removal never is: the imprisoned player holds the key, since they can spend a card of their own to point a spell at the locked creature and walk it out. The tension is deliberate. A permanent untap-denial would be oppressive, so the sacrifice trigger hands the defending side an interactive out while still demanding they pay for it. It also rewards the caster for choosing a target the opponent will not want to spend a spell on: a vanilla beater, an already-spent attacker, a creature whose abilities are not worth saving. Cast on the right body, those two mana buy a durable soft-lock that frees up your own turns; cast on a creature the opponent was going to target anyway, it is a card they get for free.