Lay Down Arms

White has always paid a premium to remove a creature permanently: exile, unlike destruction, dodges regeneration and death triggers, and white's cheapest exile answers historically carried a caveat (a delay, a return clause, a tapped-only restriction). This one hands you clean, one-mana exile with the ceiling written into your own board. The number of Plains you control is the throttle: on turn one it barely clears a mana dork, and against a Wastes-heavy or nonbasic manabase it can whiff on almost anything, but in a devoted mono-white shell it scales into a genuine catch-all that eats midrange threats without ever asking for more than a single white pip. The three life the target's controller gains is the concession that pays for the rate, a small drain-reversal that matters against aggressive decks and is a rounding error against slower ones. What that clause really does is discourage stapling the spell into the aggressive white deck it looks built for, and reward the grindier build that wants Plains counts high anyway. It is a design that ties the answer's power to a deckbuilding commitment rather than to a fixed rate, which is the mechanism that lets a one-mana exile spell exist without warping every white deck it could slot into.