Synod Artificer

Commander is where Synod Artificer earns its slot — artifact-heavy decks are ubiquitous, and the ability to tap down a table's worth of mana rocks at instant speed is genuinely disruptive at a format where Sol Ring is in almost every deck. Outside of Commander, Synod Artificer is legal in Legacy, Modern, Vintage, and Oathbreaker, but it sees essentially no competitive play in any of them — the body is too small, the mana investment too slow, and the payoff too situational compared to what those formats demand. Oathbreaker is the closest cousin to Commander in terms of artifact prevalence, so the same synergy logic applies at a smaller scale.