Boon of Emrakul

The +3/-3 split is one of black's oldest tricks for dressing up removal as a buff: the toughness reduction is the whole point, killing anything with three or fewer toughness outright, while the +3 power is a near-irrelevant rider that occasionally lets the aura turn a survivor into a finisher. As an Aura, it pays the structural tax black's "shrink" effects almost always carry. A spot-removal spell at instant speed answers a creature cleanly and leaves nothing behind; binding the kill to a permanent means you eat card disadvantage if the target is bounced or sacrificed in response, and the enchantment goes to the graveyard as a state-based action the moment its host dies. Black has worked this template repeatedly, trading toughness for an enchant-creature shell rather than the burst of a one-shot spell. What distinguishes this one is the symmetry of the numbers (three and three, costing three) and the gap it carves at the top of the toughness curve: anything with four or more toughness shrugs off the kill and simply keeps the +3 power, with the Aura staying attached. That outcome is not a failure state so much as the design's honest edge case, the partial answer that rewards reading the board before you commit. The card reads as a hard kill on most early bodies and a slightly awkward pump on the few that outlast it.