Mutilate

Scaling a board wipe to your land count is a design lever Wizards rarely pulls, because it ties the sweep's strength to commitment rather than mana spent: pour every land into Swamps and this clears almost anything; splash a second color and it shrinks to a glorified shrink spell. That mono-black tax is the whole bargain. Where a flat -X/-X effect like Languish promises a fixed answer, this one rewards the deck that has already agreed to play one color and run a basic-heavy manabase, then punishes the deck that hedged. The asymmetry inside the symmetry is the trick: it hits your creatures too, but a control or attrition shell that holds its board back while the opponent overextends turns the toughness reduction into a one-sided judgment. It also stacks with itself and with other persistent debuffs across a turn, since each casting applies a fresh round of -1/-1 counters' worth of stat loss (not literal counters, just an until-end-of-turn modifier), so a deck that can chain two sweeps clears far past what a single resolution suggests. The constraint and the payoff are the same number, and that is what makes it a deckbuilding statement rather than a card you slot anywhere.