Reciprocate

In Commander, Reciprocate is a narrow but efficient piece of spot removal — the exile clause matters in a format full of graveyard recursion, and one mana leaves you open on every opponent's combat step. The constraint that the creature must have already dealt you damage limits it to a reactive role, which makes it worse in heads-up scenarios and better in games where at least one player is attacking into you each round. In Legacy and Vintage it's technically legal but strictly outclassed by Swords to Plowshares, which has no conditional trigger and still costs one white. Modern is the same story — Path to Exile sets the baseline, and Reciprocate doesn't come close.