Languish

Black has always priced its symmetrical board wipes a notch below white's, and the minus-four cap is how it pays the difference. Where Wrath of God charges four mana to kill everything dead, this charges the same four to kill almost everything: it scoops up the entire weenie curve and most midrange threats while leaving the fattest finishers standing. That is exactly backward from how white sweepers behave, and exactly right for the deck running it. A black control shell tends to field few creatures of its own, and the ones it does field can be built to sit above the threshold; a body with five or more toughness shrugs off a minus-four pass entirely. The toughness line turns a symmetrical effect into a quietly asymmetric one without ever printing a clause that says so, and it rewards sequencing: land a creature that survives the modifier, cast this, and the board belongs to you. The design space here is the size of the modifier itself. Shift the number by one and you have a meaningfully different card, which is why so many black sweepers are variations on this dial rather than this exact setting. Minus-four lands squarely on the early-game-to-midrange band most aggressive decks live on, which is the precise reason it is both a clean answer to those decks and a poor one against anything built tall.