Iron Spider, Stark Upgrade

The tap ability is the engine, and it scales with the exact thing that makes it worth building: a board of artifact creatures and Vehicles all grow together, every turn, once the body has resolved. The wrinkle is that the counters it distributes are the same currency its draw ability consumes. Spend two mana, pull two counters off your artifacts, and you have converted board size into cards, so the deck has to choose turn by turn whether it is growing or refueling. The counters serve double duty: they are simultaneously the payoff and the fuel, which means a wide artifact board is both the thing you are pumping and the thing you are cashing in. Vigilance is the small hinge that lets the two halves coexist, freeing the 2/3 to attack without surrendering its tap for the accumulate phase. It sits in the lineage of artifact "lord" effects that reward going wide with metal, but it runs the counter-based version rather than the static-anthem version, and that distinction matters: counters persist through removal on the source and can be moved around, where an anthem evaporates the moment the anthem dies. It asks for a specific commitment (artifact creatures and Vehicles, ideally cheap and plentiful) and repays that commitment with a self-contained grow-or-draw loop that needs no other cards to spin.