Depressurize

Killing a creature by shrinking its power to nothing is an old trick, but this one refuses to be a clean removal spell: the destruction only fires if the target's power actually reaches zero or below. A -3/-0 swing erases small creatures and mana dorks outright, but it does nothing to anything with four power or more except sap it for a turn. That conditional is the whole balancing act. You are not paying two mana for guaranteed removal; you are paying for a debuff that upgrades itself into a kill only when the target is small enough to warrant it. It reads as strictly worse than a proper removal spell against the threats a black deck most wants gone, and it is: this is meant to punch down, clearing the early curve and blunting go-wide starts rather than answering a finisher. The instant speed matters more than the size cutoff suggests, though. Because the power reduction and the destruction check happen in the same resolution, casting it during combat can drop a blocker's power to zero or below or shrink an attacker out of lethal range and, when the math lines up, kill it in the process. It is a combat-trick-shaped removal spell that only rewards you when the creature it targets was never big to begin with.