Miirym, Sentinel Wyrm

Every Dragon this commander watches enter comes in twice: the original resolves, then a nonlegendary copy of it lands right beside it, carrying whatever enter-the-battlefield trigger the original brought. That is the whole engine, and it is a doubling effect built specifically around a tribe that already runs heavy on beefy bodies and stacked entry triggers. The nontoken restriction is the balancing clause worth reading closely: cast Dragons and cheat them into play, and each one forks; make tokens off something else, and those do not chain into infinity. So the deck it wants is a build that keeps casting or reanimating real cards rather than flooding the board with copies, which keeps the payoff tethered to actual investment. The nonlegendary exception on the copies matters too, since it dodges the legend rule that would otherwise delete a duplicated legendary Dragon on sight, letting even singleton legends double freely. Ward on a six-mana 6/6 flier is modest protection, enough to tax a removal spell without pretending to be untouchable. The color identity (Green, Blue, Red) reads unusual for a Dragon leader, but it is the exact set of colors that supplies the ramp, the recursion, and the flicker effects that turn a single trigger into a runaway board, which is precisely the point.