Dark Betrayal

Black removal almost never restricts itself by who or what it kills: the color destroys creatures regardless of controller, and that indiscriminate reach is part of its identity. So a one-mana instant that destroys only a black creature, and nothing else, is a deliberate inversion of how the color normally operates. The payoff for that severe restriction is the rate. Inside its window there is no toughness ceiling and no "can't be regenerated" rider to pay for, because the entire price of the effect is folded into the target line: every nonblack creature on the battlefield is simply immune, and that immunity is the cost. The restriction keys off the creature's actual current color, not merely what is printed in the corner, so color-changing effects and other characteristics that alter a creature's color move it in and out of range: a black creature turned white slips free, and a nonblack creature painted black becomes a legal target. This is the design economy anti-color cards have always run on: you accept that the card is a blank against most of the table in exchange for a price nothing fairly costed could match. What makes it a cleaner specimen than most is the mirror-tinge of the target, hate pointed at a creature your own color would happily cast. It answers exactly one color, and that color is its own, and it apologizes for neither half of the bargain.