Tainted Remedy

Lifegain reads as purely defensive: it buys time, blunts aggression, fuels payoff engines. This enchantment treats that buffer as a liability and inverts the replacement effect that governs it, so the opponent's safety valve turns into the thing that drains them. The cleverness is in the specificity: it does not touch life payment, only life gain, so it is the lifelink swing, the Sphinx's Revelation, the incidental creature-and-spell drain riders that turn lethal the instant they resolve. A player accustomed to stabilizing through gain finds the act of stabilizing is what kills them. Because the redirect only ever applies to opponents, it never complicates your own clock; it sits as a standing tax that keeps applying every turn it stays in play. The cost of that elegance is dependence: against a board that races with creatures alone and never reaches for a single point of life, it is a blank, which makes it a hate piece wearing a build-around's clothes (devastating against lifegain shells and life-leveraging control, inert against decks that simply do not engage). Its lineage runs through earlier life-denial designs like Sulfuric Vortex and Erebos, God of the Dead, but those clamp the spigot shut; this one reverses the plumbing and sends the flow back at its source.