Windborn Muse

Propaganda on a stick. The enchantment Propaganda taxed attackers two mana apiece in blue without ever contributing to the board; this hangs the same Ghostly Prison style tax on a flyer that blocks, races, and chips in for two on the offense. The tax scales per attacker, so it does not lock anyone out so much as price aggression: a single creature can still come through cheaply, but a wide assault has to pay a tariff before the first point of damage lands, which buys the controller the time that a swarm strategy is built to deny them. Crucially the effect protects the player, not the planeswalkers or teammates, and it stops nothing already on the stack: it is a deterrent applied at the declare-attackers step, not a fog or a wall. What earns it over a pure pillow-fort enchantment is that the 2/3 flying frame answers the game it slows down, since a Spirit taxing the ground war while threatening through the air closes things out rather than merely stalling. White had Ghostly Prison for the static version, but stapling the tax to a creature trades resilience (it dies to removal an enchantment shrugs off) for tempo and a clock, the trade-off that defines whether a defensive piece belongs in a controlling shell or a tempo one.