Mass Diminish

A single-player fog that never removes a creature, only rewrites the number. Instead of sweeping a board off the battlefield, it overwrites the base power and toughness of every creature one player controls to 1/1 until your next turn: the army is still there, still swinging, but it swings for one. The load-bearing choice is setting base stats rather than applying a minus-X penalty, which is why it scales against exactly the giant boards a mass shrink spell would struggle to catch. It does not care how large a creature was; it simply resets the floor. The important limitation is what that floor does not touch. Because base stats live in Layer 7b, any +X/+X effects and any counters apply on top of the new 1/1, whether they were placed before or after this resolves. Keywords and triggered abilities stay live too, so a trampling, flying, or deathtouch threat remains dangerous even at one power. This is arithmetic, not disarmament. The temporary duration is what the flashback answers: instead of a one-turn reprieve, you get two staggered windows, the second cast whenever the rebuilt team threatens again. And the aggressive line is the one worth learning: flatten a defender's blockers to 1/1 before your own oversized creatures attack, and a locked ground stall becomes lethal in a single combat step.