Shivan Branch-Burner

Seven mana for a 4/4 flier with haste is a rate no aggressive deck would pay at face value, and the printed cost is a ceiling that convoke exists to undercut. Each generic pip can be paid by tapping any untapped creature, while a red pip needs a red creature, so the discount scales with how wide the board already is when the spell goes on the stack. That timing is the design's real hinge. Convoke is applied as part of casting, and every body committed to paying is locked down for the turn, meaning none of them will swing in the combat that follows. What you are buying, then, is a trade: several creatures stay home this turn to conjure an evasive threat that attacks immediately. Flying and haste make that trade worth taking, converting the saved mana into four damage in the air on the spot rather than a fat body that idles until it untaps. Convoke has usually been welded to go-wide token strategies that empty their hand cheaply and win on the ground; bolting the keyword onto a beefy Dragon points it somewhere blunter, giving a swarm deck a top-end finisher it can deploy without ever assembling seven lands. The more bodies willing to tap out for a beat, the closer this reads to a two- or three-mana haymaker, and the whole design leans on that crowd being present, and expendable, the moment it hits the stack.