Cliffhaven Vampire

The lifegain payoff that turns incidental healing into a clock. Most cards in this vein cap the conversion (gain a life, scry a card; gain life, draw once a turn), but here the trigger fires on every life-gain event and drains an opponent for each one, with no upper bound and no cost beyond actually gaining the life. That uncapped repeatability is what gives it teeth: a single Soul Warden-style trickle becomes an attack on an opponent's total each time it resolves, and any lifelink attacker or sacrifice-fueled gain effect quietly doubles as an assault on the life you are trying to lower. The 2/4 flying body keeps it earning its slot without demanding attention: it blocks early and chips in the air, which matters for a card whose real work happens off your other permanents rather than in combat. The wording "each opponent loses 1 life" rather than "target opponent" is the choice that ages well; it scales with the table instead of picking one victim, which is exactly the kind of multiplayer math a four-mana engine wants on its side. It asks only that the deck around it gain life on purpose, and it converts that intention into a win condition that ignores the board entirely.