Soul Warden

The original lifegain trigger, the one every successor has been priced against. The design idea is almost embarrassingly simple: a one-mana body that taxes the act of putting creatures onto the battlefield, your own as much as your opponent's, by skimming a single point of life off each one. That symmetry is the engine. The card does nothing in a vacuum, but flood the board and it converts every token, every recurred creature, every cheap go-wide play into a stream of life that scales with the table rather than with the card itself. The shape has been refracted more than once: Soul's Attendant is a near-identical reprint, Essence Warden flips it to green, Suture Priest bolts on the punitive half. None displaced the original, because the original already nailed the cheapest viable version of the effect. The reason it endures is that it scales with two things at once: board width and the time the game runs long. A 1/1 that costs a single white mana threatens nobody, which is precisely why a lifegain engine can sit on it without warping the rate. The body is the disclaimer; the trigger is the card. Aristocrats and token strategies across many years have been measured against whether they could afford to run it, and most of them could.