Hell Swarm

The zero-toughness half of the effect is the tell, and it is the whole story. This is not removal and cannot pretend to be: a -1/-0 effect leaves every creature alive, only sapping power until end of turn. What it does is rewrite combat math for a single black mana at the moment of attack, shrinking attackers below the damage they need to trade up, flattening a wide board of one-power creatures into harmless bodies, or knocking a swarm of one-power creatures down to zero damage on the swing. The symmetry is the friction that prices it: hitting your own board as well as theirs means the card only advantages you when the opposing creatures are doing the attacking or the relevant work, which narrows it to a defensive trick rather than a tempo play. It dates from early in black's relationship to combat, when the boundaries of the color's reach there were still being mapped out, and the answer it offered (a one-mana, board-wide, symmetric power reduction) sits oddly between a true combat trick and a control tool, too small to dominate either role. The card captures an old design instinct: black as the color of universal degradation, willing to touch its own creatures to drag the opponent's down. The color eventually found cleaner combat-shaping language elsewhere, and this early experiment in mass debuffing quietly fell out of the conversation.