Scent of Nightshade

The trade here is information for power: the more black cards you show, the bigger the shrink, and the reveal mechanic is doing real design work. Unlike a fixed-cost kill spell, this scales with a resource you have already gathered (the density of black cards in your hand), spending nothing but knowledge. You reveal the cards rather than discard them, so the cost is purely the hidden information you give up, which makes the card a strange hybrid of removal and tell: a deep mono-black hand can flash this for a lethal minus, but you have just told your opponent exactly how stocked you are. This is one of black's recurring experiments with variable-power removal, where the answer's effectiveness is gated behind a resource other than mana. The -X/-X structure means it scales toward toughness as well as power, so it can drop a creature below the threshold it needs to survive combat or block, all at instant speed and only for the turn. That until-end-of-turn clause is the quiet discipline on the whole thing: this kills by reducing toughness to zero, not by stapling a permanent debuff, so a body that survives the swing pops back to full next turn. The catch is the obvious one: a single-card reveal buys you a -1/-1 that rarely matters, so the spell earns its slot only when you have committed hard enough to one color to make the reveal hurt.