Fatal Fumes

Toughness reduction is the half of creature removal that always reads worse than a clean kill, and four mana for -4/-2 is a clean illustration of the math problem. The -2 is the operative number: shaving a body two toughness answers a one- or two-toughness creature outright and drops everything taller into combat range rather than killing it on the spot. A four-toughness blocker survives with two left; the power swing matters less than that toughness ceiling. The split stat exists to dodge comparison to a symmetric -X/-X effect, which at this cost would read as too efficient, but the asymmetry just narrows the use cases instead of paying for them. Toughness reduction does earn a corner that destruction cannot reach, namely indestructible creatures, where shaving the body to zero ends them while a destroy effect bounces off; note it does not skip death triggers, since a creature reduced to zero toughness still dies and still fires its abilities. The instant timing buys a combat ambush, but it is an expensive one, and black's own removal palette (cheaper destroy spells, edicts that force a sacrifice, the deeper -X/-X effects) covers most of the same ground at a better rate. What is left is midrange filler: a soft, conditional answer that wants the body small and the timing to be combat, and asks for nothing more than a slot in a removal-light deck that ran out of better black spells.