Feebleness

The flash is the whole reason this exists rather than living as another sorcery-speed creature shrinker. Holding it back turns -2/-1 from a deckbuilding cost into a combat ambush: drop it on a blocker mid-combat and your attacker punches through a body that just got two power and one toughness smaller, or hang it on an attacking creature so it deals less and dies more easily to your blocker. The numbers are deliberately asymmetric. The -1 toughness is small enough that it rarely kills outright, but the -2 power is the part that does the work, neutering an aggressive two-power one-drop into a do-nothing or shaving enough off a fattie that a chump trades up. It is a debuff that wants the creature to keep living, ideally as a permanent liability stapled to the board rather than a clean removed threat. That is the tension early black designers kept circling with this style of Aura: a removal-adjacent answer cheap enough to maindeck, but soft enough that it never fully erases a creature the way a kill spell does. Pacifism handles the high end by shutting off attacks entirely; this handles the low end by quietly making a small creature stop mattering, at instant speed, for a price you can afford to leave open.