Mists of Littjara

The trick here is the -0. Most defensive combat tricks that shrink an attacker do it by knocking down power and toughness, which means they double as removal in the right window; this one refuses to touch toughness at all, and that refusal defines what the card can and cannot do. A blocked or unblocked attacker keeps its full toughness, so the effect never trades up into a kill: it exists purely to blunt damage. That narrowness is what buys the flash. A -3/-0 at instant speed is a clean way to ambush an alpha strike, fog down the biggest threat in a swing, or flip a race by three life without ever putting the creature in the graveyard. It also folds into a longer game as a permanent tax, since as an Aura it stays put and keeps the enchanted attacker three points quieter every combat rather than resolving once and vanishing. The Vehicle clause is the quiet tell of a modern-era printing: crewed Vehicles attack as creatures, so a power-only debuff that can latch onto one answers a threat older shrink effects simply could not see. It is a card built to survive combat, not win it, and the -0 is the line it is never allowed to cross.