Unleash Fury

The pump spell that scales instead of adds. Where Giant Growth and its many descendants hand a creature a flat bonus, this one multiplies whatever the creature already brings to the fight, which makes it dead weight before you have built a threat and a game-ender the moment there is a real one to point it at. That is the whole design tension: it costs almost nothing and does almost nothing until you have already assembled the thing it doubles. On a 2/2 it is a modest trick; on a trampling fatty or a creature that has already grown through counters or anthem effects, it converts a comfortable board state into a lethal one in a single instant-speed window. The doubling also plays cleanly with power-referencing effects downstream, since the boosted number is what other cards read for the rest of the turn. Compared to the additive tricks it shares a slot with, the mana efficiency is deliberately lopsided: the flat pumps are honest at every stage of a game, while this one is priced to be feeble early and absurd late, asking you to hold it until the board makes it worth casting rather than fire it on curve.