Plumb the Forbidden

The trick is in the copy trigger, not the base spell. Cast on its own, this is a strictly worse card draw: two mana to draw one and lose a life is a rate nobody pays. The additional cost rewrites it entirely. Sacrificing creatures copies the spell once per creature, and because the copies are made by a triggered ability rather than the cast itself, each copy resolves as its own draw-a-card, lose-a-life event. That structure lets it function as a sacrifice outlet with no ceiling: dump a board of tokens in response to a wrath, in response to targeted removal, in response to your own upkeep trigger, and turn a pile of creatures about to die anyway into an equal pile of cards at instant speed. The life loss scales with the draw, which is the honest cost: the more you convert, the deeper into your own life total you dig, and there is no way to draw the cards without paying it.

The instant speed is what makes it more than a one-shot sacrifice payoff. Available on the opponent's turn, mid-combat, or on the stack in response to whatever is trying to break up your board, the outlet arrives exactly when board presence is about to become worthless. Aristocrat decks had long wanted a free outlet that also refilled the hand; the sacrifice-to-copy structure delivers both in a single card, converting creatures into cards at the precise moment those creatures were headed for the graveyard anyway.