Warning

Fog answers a board; this answers a creature. That narrowing is the entire pitch. Where green's full-stop prevention effects neutralize an alpha strike for cheap and stay broad and reactive, this points at exactly one attacker and lets the rest of combat play out normally: your blockers still trade, your other defenders still take damage. It is prevention, not removal, so the creature survives to swing again next turn; you are renting a single turn of safety against one body rather than solving it. The instant-speed window is the appeal. Hold up a lone white mana, watch the attack step develop, and decide whether the threat that actually got pointed at you is worth the answer. White has a long history of this kind of targeted combat-damage prevention, and the design here is unusually unencumbered: no upkeep tax, no caveat, no fine print. The limitation is the honesty. It does nothing against noncombat damage, nothing against a wide attack, and nothing to change the board state. Because the attacker lives, you trade a card for time instead of a one-for-one: the inherent disadvantage of a fog, focused down to a single creature and priced at one mana.