Vivisection

The price of the card draw is the whole equation here: three cards is a steep dig for blue, and the discount comes from feeding a creature to the spell rather than paying full mana for the privilege. That sacrifice clause is not a downside to route around; it is the engine. The card was built for decks already generating bodies they want dead, where the creature on the chopping block is a token, a creature whose enters-the-battlefield value has already been banked, or one tagged for a death trigger anyway. In that shell, you are not losing a creature to draw three; you are cashing one in twice. The blue-black aristocrats lineage has always wanted effects that turn a sacrifice into raw card flow rather than incremental life-drain, and this sits squarely in that tradition: the rate looks unremarkable until the thing you sacrifice was a liability or a payoff in its own right. Outside that context, paying a full creature plus four mana for three cards is a bad deal, and the spell does nothing to hide it. The asymmetry is the point: cheap for the players who pay the additional cost for free, overpriced for everyone else. That split is exactly what a sacrifice-additional-cost card is supposed to enforce, and it sorts the deckbuilders who can feed it from the ones who would be better served by a plain Divination effect.