Saheeli, the Gifted

Both plus abilities feed the same loop. The first builds an artifact board one Servo at a time; the second turns that board into a cost reduction on your next spell, so the more artifacts already on the table the cheaper the next threat becomes. Where most planeswalkers protect themselves by generating value, Saheeli protects herself by generating fodder that is also fuel, and the two plus abilities are worded so you can only pick one per turn: a Servo now, or a discount now, never both at once. That constraint is what keeps the engine from running away on the turn it lands. The ultimate is the payoff for having spent those turns hoarding artifacts, doubling every artifact you control for a single hasty swing before the copies vanish, which rewards the wide, token-heavy board the plus abilities were already assembling. Her commander eligibility completes the design: an artifact-matters commander that sits at four mana in Izzet colors, cheap enough to redeploy and built to headline a deck where every Treasure, every Servo, every equipment counts toward the discount, and the artifact creatures also count as bodies. She is less a value planeswalker than the centerpiece of an affinity-adjacent artifact deck folded into the command zone.