Exquisite Blood

Half of a two-card combo whose other half is the only reason most people own it. On its own, the trigger does no losing: it watches for an opponent's life loss and converts it into life for you, a passive drain-deterrent that quietly accrues a buffer in grindy attrition decks without ever closing a game. It is not a lifegain payoff; it is an opponent-life-loss payoff that happens to pay in life. The whole identity lives in what it pairs with. Sanguine Bond mirrors the direction: it watches your lifegain and converts it into an opponent's life loss. Run both and the loop closes on itself: one point of life loss feeds this enchantment, which gains you life, which the other converts into more life loss, which feeds this one again, repeating until an opponent reaches zero. The loop is symmetrical and self-sustaining, indifferent to how the first point of damage lands; it only needs the cycle started. That is what makes the combo both clean and despised: it converts any single point of incidental drain into a full kill. The dependency cuts both ways. Alone, the card reads as a slow incidental life cushion in a black drain shell. Next to its mirror, it becomes one of the most reliable two-card kills the color offers, which is why any deck running it is implicitly running the tutors to assemble the other half.