Lantern Flare

Two mana buys a token deck a one-sided Fireball scaled to its own board: point it at a blocker or a planeswalker, deal damage equal to your creature count, and bank that much life on the way. Fund it with mana instead of bodies and the bracketed clause vanishes, promoting X into a variable you pay for directly; the spell steps into Boros and becomes a scalable burn-and-lifegain effect that no longer needs a single creature in play. The design worth studying is how the two costs answer opposite board states. The white price rewards a wide, committed board and does nothing off an empty one. The alternate cost bails you out precisely when the white mode would do nothing: after a sweeper, on a stalled draw, in the games where you have the mana but not the creatures. Most cards with this keyword strip a restriction to widen a single effect; this one strips a restriction to swap which resource pays for the effect, trading board presence for mana. That is a quieter use of the mechanic than its splashier printings suggest, and a more instructive one: it uses the second face not to do more, but to do the same thing from an entirely different deck.