Wring Flesh

The asymmetry in those numbers is the whole design. Three points of power-reduction for a single black mana is a lot of combat-shrinking, enough to bounce most early attackers off a blocker or flip a would-be profitable trade into a one-sided one. But the toughness only drops by one, so this kills almost nothing outright: a 1/1 dies, a 3/1 dies, and anything with two or more toughness just shrugs and lives. That split is what keeps a one-mana instant from being premium removal. It is a combat-trick first and a kill spell only at the margins, and timing is the whole skill: cast it before damage to undercut an attacker's power and turn a bad block good, or cast it after damage to finish off a creature already chipped down to its last point of toughness. The lineage is old; this kind of black "weaken" effect goes back to the earliest sets, where shaving an attacker's power was how black handled creatures it could not destroy outright. Weakening rather than killing reads as a downgrade now that efficient unconditional removal is cheap, but it does carry one quiet edge: because it changes a number instead of checking a state, it can put down a regenerating or indestructible creature that happens to sit at exactly one toughness, where a destroy effect would bounce off entirely. A narrow tool, built for a deck that wants cheap interaction at instant speed and has its own clock to close out the creatures this only bruises.