Righteous Blow

The single white mana buys you damage only when a creature is committed to combat: no attacker, no blocker, no target. That restriction is the whole bargain. Stripped of combat, this is a dead card in hand; inside the combat step, it is a one-mana Shock that punishes the attacker who overextended or the blocker who stepped in front of your creature. The window is narrow and the design knows it, pricing the spell as cheaply as a single colored pip can go precisely because it can do nothing on the opponent's empty board. White's removal has always leaned on this kind of conditional efficiency, trading flexibility for rate: it answers what is on the table at the moment of conflict rather than offering open-ended reach. Two damage clears the small creatures that anchor aggressive starts and trades up against anything in the same range that wandered into a bad block. The reward for accepting the combat-only clause is that you can hold it almost free and let the opponent's own attack or defense decide when it fires.