Blade Banish

The power-4 clause is the whole design bargain. Exile is the cleanest removal a color can offer: no death triggers, no recursion, no counters to dodge, and white pays a premium for that finality. Rather than gate it behind a high mana cost alone, this restriction sizes the answer to a specific class of threat, the fatties and finishers that four power tends to mark, while leaving the small utility creatures, mana dorks, and one-drop hatebears untouched. That is a deliberate seam in the design: it will not help you against a swarm of tokens or a two-power aristocrat engine, but the moment an opponent commits a real haymaker, it erases the thing permanently at instant speed. The instant timing is where the price earns back some value. It lets you hold up the answer through a combat step, exile a blocker mid-attack, or wait for the opponent to sink resources into a threat before removing it from the game entirely. White's clean-exile removal has always come with a hedge of some kind (a lifegain rider, a sorcery-speed limit, a cost that scales), and here the hedge is simply that the target has to be big enough to matter. It is a spell built to punish the top of an opposing curve without answering the bottom of it.