Darien, King of Kjeldor

Most legendary creatures want to keep you out of harm's way; this one turns getting hit into a recruiting drive. The trigger is the whole design conceit: every point of damage dealt to you becomes a 1/1 Soldier, so the math runs backward from how the game normally treats incoming combat and burn. A burn spell to the face mints an army. A swarm of attackers that connects builds the defender a bigger swarm in return. The build-around lives in finding a repeatable way to take damage on your own terms (a source that pings you for one or two each turn), at which point the 3/3 body stops being a curve-topper and starts being a generator. Note the precise wording, though: the engine needs damage, not life payment, so the self-inflicted loss from fetch lands or other life-as-a-cost effects does nothing here, and the trigger only counts damage dealt to you, not to creatures or planeswalkers you control. The tokens also arrive after the damage resolves, never before, so they cannot block the hit that makes them. White rarely gets to profit from taking damage, and almost never at this scale; the card sits at the seam between the color's go-wide token tradition and a damage-conversion idea that usually belongs to black or red. It rewards a deckbuilder willing to weaponize their own life total, which is precisely the trade white is not supposed to be able to make.