Deal Gone Bad

Four mana at instant speed to shave three points off a creature's toughness is a rate you would never pay in a vacuum, which tells you the -3/-3 is not really the point. The mill three is bolted on as a second target, and the two halves need not touch the same player: shrink an attacker on the opponent's side, feed cards into a graveyard you actually want stocked, and the spell does two jobs on two players in one instant-speed window. That split-target construction is the whole design logic. As pure removal it is soft (three toughness is a real ceiling, and creatures grow past it), so the card only earns its cost when the mill matters, whether that means self-mill to fuel a reanimation or graveyard payoff, or clock-mill against a deck racing its own library. The instant timing lets it sit up as a combat trick that also advances a mill plan, collapsing two turns of setup into one. It rewards a build that treats the graveyard as an asset rather than a liability, and does little for one that treats the yard as a dumping ground.