Wine of Blood and Iron

Power-doubling is a fragile thing to put on an artifact, and this one solves the fragility problem by refusing to last. The math is brutal in the right configuration: a creature with power five becomes a ten, and feed it the activation twice in a turn and the additions compound off the new power each time, so a modest attacker can balloon into a one-shot kill before damage. The catch is built into the card rather than the cost: it sacrifices itself once it has done its work, so this is a single-turn detonator, not a permanent enchantment-style buff. That self-destruct clause is the entire design. A reusable power-doubler would be an Overrun engine; a self-immolating one is a finisher you cash in exactly once, which is why the four-mana activation cost feels almost incidental next to the sacrifice. It wants a creature already large or already evasive, applied on the turn the game can end, and it punishes greedily holding it for a better board that never comes. The artifact frame matters too: colorless power amplification slots into builds that have no business doubling a creature's strength by their own color identity, which is the quiet reason a device like this gets remembered long after its set fades.