Spontaneous Mutation

Pseudo-removal that scales with the one resource most blue decks are throwing away anyway. The -X/-0 clause does nothing about a creature's ability to block or survive: it strictly subtracts attacking power, which makes this a combat answer rather than a kill spell. That narrows it to a defensive role, and the flash timing is what makes that role work. Cast in the attack step, after blocks are declared or before damage, it turns a lethal swing into a whiff or shrinks a threat below the size it was built to clear. The graveyard-as-fuel design pairs that timing with self-mill and cheap cantrips: the more spells already churned through, the larger the penalty, so a deck that loads its yard early can neuter an attacker for a single mana by midgame. As an Aura, the reduction is continuous rather than a one-turn shrink: as long as it stays attached and the graveyard stays full, the creature keeps fighting at the reduced power, and the penalty only deepens as more cards pile up. The tension is that the effect is cosmetic against anything that wins without attacking, and a single bounce or removal spell resets the math entirely. That is the cost of pricing a flexible, scaling combat trick at one mana and refusing to let it touch toughness. It is a reactive tempo tool dressed as an Aura, built for blue decks that already want a full graveyard for other reasons.