Bind the Monster

One mana to park almost anything on the board, with the price written into the trigger: the enchanted creature deals damage to you equal to its power the moment the Aura resolves. That clause is the entire balancing act. Against a small threat the tax is trivial; against the giant you most want to neutralize, it can be a serious life swing, and it never scales down. The design turns the classic pacifism problem (a cheap answer that permanently disables a creature invites abuse against expensive threats) into a self-correcting cost: the bigger the thing you lock down, the more it hurts to do so. Because the creature is tapped on entry and then forbidden from untapping, this doesn't kill anything; it parks it, which leaves the door open to bounce, blink, or an untap effect undoing the whole arrangement. The lineage is old, cheap blue disable auras reaching back to the earliest sets, but the damage clause is the modern refinement: instead of a flat drawback or a conditional trigger, you pay in your own life total, up front, for the exact amount of power you are neutralizing. Playing it early against a small board costs almost nothing; holding it for the finisher costs plenty, which is precisely the tension a one-mana answer this efficient needs to carry.