Canopy Gargantuan

The upkeep trigger reads like a runaway function: it does not add a flat counter or double a stat, it grows each other creature you control by its current toughness. Turn one after this resolves, your 3/3 becomes a 6/6; the turn after, that 6/6 becomes a 12/12, and the curve steepens every step because the amount added is itself the number that keeps climbing. That compounding explains why the trigger sits on the upkeep rather than at combat: it wants a board that survives to your next turn, which is where the 7/7 flyer earns its cost. Ward is the specific tax that protects the engine, not the body: at seven mana the Dragon is not hard to kill, but forcing an extra two mana onto every removal spell that targets it buys the one upkeep you need before the snowball becomes lethal. The design lineage here is toughness-matters as an offensive resource, a thread green has flirted with through cards like Doran, the Siege Tower and various defender payoffs, but those read toughness once for damage. This reads it recursively, converting a defensive stat into permanent power turn after turn, so wide boards of small, high-toughness bodies convert faster in aggregate than a single fatty ever could. The 7/7 flying frame is almost incidental; the real payload is what the second creature onward does to your board math.