Neriv, Heart of the Storm

Damage doublers usually live on artifacts or enchantments that sit back and pump every attacker: Gratuitous Violence and its lineage. This one narrows the payoff to a single class of creature (anything that entered this turn) and hangs the doubler off a 4/5 flying body, and that narrowing is what makes it play so differently. The reward is not "your board hits twice as hard"; it is "the creatures you just committed hit twice as hard," which flips the usual math on tokens, blink triggers, and haste threats. A freshly cast attacker, a token spat out by a trigger, a hasty dragon crashing in the turn it arrives: those are the payloads. The board that stuck around from last turn, including Neriv itself the turn after it lands, gets nothing. The clock resets each turn to whatever you can put down fresh, pushing toward a commitment-forward, tempo-positive style rather than a wide static board. The Mardu color identity does the rest, pointing at aggressive, sacrifice-adjacent shells where a stream of new bodies is the plan anyway. Flying earns its slot too: it keeps Neriv relevant as an evasive attacker even on the turns its ability doubles someone else's damage, since the doubler does nothing for its own body once that body has been down since last turn. The interesting arithmetic is never on the dragon; it is on everything you deploy the moment the dragon is already in play.