Atalya, Samite Master

The X here drains your white mana into one of two banks: a single-shot damage prevention shield for a creature, or a flat lifegain payment that can sink an entire turn's worth of Plains. What separates it from the run of lifegain effects of its era is that the cost is a generic X spendable only as white mana, so the ceiling scales with how much white you can dump, and the activation repeats each turn the tap is available. The prevention mode reads as defensive utility, but the design's real pressure point is the conversion: with enough white mana, an untapped Atalya turns mana into life by the bucket, the sort of arbitrary lifegain that combo and pillowfort builds have always wanted as an outlet rather than a wall. The 2/3 body is deliberately unthreatening, a Samite Master in the literal sense (the white-aligned damage-preventer lineage stretching back to Samite Healer), positioned as an engine piece you protect rather than a clock you race with. The white-only restriction sets the price for that scale: you pay in deckbuilding commitment, not in mana efficiency, so the card demands a heavily white manabase to do anything impressive and quietly does nothing in a deck splashing white for a single spell.