Vanquish the Weak

The power-3-or-less clause is the whole design problem, and at three mana it is not a bargain: unconditional instant-speed kill spells sit at this cost too, so this one pays the same price while accepting a hard cap on what it can point at. That inversion is the point. Where Doom Blade and Go for the Throat carry narrow type exclusions but no size limit, this spell does not care what the creature is, only how hard it hits. It cleanly answers mana dorks, aggressive two-drops, and the bulk of utility creatures, then folds completely against the fatties and finishers a control deck most wants gone. Small-creature removal is territory black already owns at lower cost (Disfigure, Fatal Push, Dead Weight all do this work more cheaply), so the interesting question is why a three-mana spell would accept the same restriction those cards carry for a fraction of the mana. The answer is that it belongs to a family of conditional black kill spells whose window narrows as the board grows: a spell that gets steadily worse the more dangerous the game becomes. That is honest color-pie discipline, not a flaw, but it also explains why the power cap has to be generous enough to catch a wide early curve to justify the rate. When the trade is a full unrestricted removal price for a spell that shrinks against the very threats it was cast to stop, the restriction has to earn its keep on volume of small targets rather than on efficiency.