Red Guardian, Super-Soldier

Removal gated behind aggression is a rare shape in white, and this is a clean expression of it: the destroy trigger only fires on a creature that has already dealt damage this turn, so the card punishes what an opponent's board did rather than what it threatens to do. That constraint does all the work. It cannot answer a blocker sitting back, cannot break up a defensive wall, cannot preemptively clear a threat before it swings, and cannot even catch an attacker mid-combat before damage resolves. What it does instead, thanks to flash, is turn a completed attack into a liability: an opponent's creature connects, and any time after damage you can flash in a 2/2 at instant speed and destroy it, leaving your body on the board. The timing is the point. Held up during an opponent's turn, it trades up after combat while sticking around; cast on your own turn, it is a much narrower spell, since it needs an opponent's creature to have dealt damage first, which usually means it has been holding for combat all along. White has always leaned on conditional, symmetrical answers, and pointed one-sided destruction is usually red or black territory. Bolting the removal to a damage clause is how the color earns access to it: you get to kill nearly anything, but only after it has already bitten someone, and only if you had the three mana open to spring the response.