Sleeping Potion

Tapping a creature down is the easy part; keeping it tapped is where most prison effects either overcommit or fall apart. This one threads the needle with a sacrifice clause that fires the moment the enchanted creature gets pointed at by any spell or ability, which is both its weakness and the reason it stays cheap. The lock holds against opponents who simply leave the creature alone, but it dissolves the instant anyone targets it: a bounce spell, a pump, even the controller's own removal aimed at the Aura's host all trigger the sacrifice and free the prisoner. That makes it a softer prison than a true tapper, since the trigger keys on becoming a target rather than on the creature changing zones or attacking, and once it fires the Aura is gone for good rather than reusable. The design lineage runs through the blue tradition of denying untaps as a substitute for the hard removal blue does not get to keep: the color answers a threat by neutralizing its tempo rather than killing it, and the fragility of the lock is the tax blue pays for reaching outside its lane. The entry tap means it can lock down an already-untapped attacker the turn it lands, but the brittleness of the target trigger means it was never meant to hold a creature an opponent actually cared about defending.