Critical Hit

Double strike as a two-mana instant is an aggressive but familiar effect; the recursion clause is what makes this one worth a second look, because it answers to a die rather than a graveyard cost, a mana payment, or a discard. Roll a natural 20 on any d20 you were already rolling for another effect, and this returns to your hand at no additional price. That folds the game's randomizers into a value engine: the same twenty you were hoping to see on a treasure-hunt or a spell-scaling roll now also refills a spent combat trick. It is a soft loop, not a reliable one. A natural 20 lands one time in twenty, so the recursion is a lottery bolted onto an otherwise ordinary pump spell, upside that arrives when the dice cooperate rather than a plan you can build toward. The honest read is that the card wants to double an attacker's damage right now, and the return trigger is a bonus. It belongs to the small family of spells that reward stacking as many d20 rolls into a turn as possible, where the recursion stops being a rounding error and becomes a genuine reason to keep rolling.