Runner's Bane

The power restriction tells you exactly who this was built to stop. Capping the enchant clause at power 3 or less aims the card squarely at the small, fast threats and utility creatures that aggressive and tempo decks lean on, while leaving the fatties for someone else. The package is unusually complete for the price: it taps the creature on entry, cashing in immediate tempo rather than waiting a turn, then denies the untap step to hold it down indefinitely. That removes one attacker and one blocker from the board for a single card, with no death trigger handed to the opponent and no creature traded away, which matters against decks built on dying-creature value where a true kill spell would do the controller a favor. The wrinkle that separates this from real removal is that the creature stays on the battlefield with all its abilities intact: any enters-the-battlefield value is already banked, and its triggered and static abilities keep working while it sits there tapped. You have frozen the body, not neutralized the card. The obvious counterplay is to bounce or sacrifice the held creature and reset it, so this lives or dies on whether the format gives opponents cheap ways to recover their stuck permanent. White has long owned this kind of soft removal (Pacifism, Arrest, Faith's Fetters); blue's version trades the can't-attack-or-block clause for a tap-and-hold, buying the upfront tempo and paying for it by leaving the creature's static effects on the table and letting any power-4 threat dodge the targeting line entirely.