Condemn

The attack requirement is the whole bargain. Path to Exile and Swords to Plowshares hit anything, anytime; this only answers an attacker, declared and committed, which makes it strictly reactive and useless against a threat sitting back on defense. What you buy with that restriction is an answer that does not care about indestructibility, regeneration, or a stat line too large to burn (though, as a targeted white spell, it still cannot touch a creature with protection from white). Bottoming the creature instead of destroying it sidesteps the death-trigger and graveyard-recursion plans that a marquee finisher leans on; it does not exile (a shuffle or a deep tutor can still retrieve it, so this is less permanent than the white one-drops it sits beside), but absent such digging it buys time before the thing can be redrawn and recast, and against a deck without a way to dig, often much longer. The lifegain rider scales to the bottomed creature's toughness, which reframes the spell against a fat attacker: you are not just removing the swing, you are gaining the life you would otherwise have lost to it, then some. That tempo swing is most of why a one-mana instant that demands an open combat step has stayed relevant in white's removal suite. It is the answer held for the creature you cannot afford to trade with, priced at the cost of letting it commit first.