Apathy

Keep a tapped creature from untapping for a single blue mana, then hand the cost of escape to its controller rather than to the caster: this is a soft Pacifism that turns a removal effect into an upkeep tax. The discard-to-untap clause is the whole design idea, and it is built to be costly to break. Each upkeep, the enchanted creature's controller faces a real choice: pitch a card they cannot choose, or leave their threat tapped for another turn. The "at random" matters more than the discard itself, since the controller cannot dump a known dead card to free the creature; they are gambling a piece of their hand they may have wanted. That asymmetry is what makes the lock bite hardest against a fatty or a value engine, the kind of single target worth grinding away at over several turns rather than answering cleanly. And the punchline runs opposite to how it looks. Against an empty hand there is no card to discard, so the optional untap is simply unavailable that upkeep and the creature stays tapped until they draw again: the lock is most secure precisely when the opponent has the fewest resources left to defend it. The friction is real (it is an Aura without flash, so it can only land at sorcery speed, and it can be dispelled), but it belongs to a line of blue tempo enchantments that buy time rather than solve problems, conditional "doesn't untap" logic priced to be escaped only at a cost the caster never has to set.