mtg march of the machines card - Machine including 1–2 card(s) of rarity Rare or higher and 3–5 Uncommon March of the Machines |

That is a neat two card combo, but we can step it up a bit more and make a more potent combo than that

Blightbelly Rat Brimaz, Blight of Oreskos Cacophony Scamp Carnival Elephant Meteor Contagion Clasp Contagion Engine Core Prowler Drown in Ichor Everythingamajig Filigree Vector Glistening Sphere Grateful Apparition Grim Affliction Gulping Scraptrap Karn's Bastion Martyr for the Cause Metastatic Evangel Norn's Choirmaster Patrolling Peacemaker Proud Pack-Rhino Recon Craft Theta Scheming Aspirant Spread the Sickness Staff of Compleation Surge Conductor Sword of Truth and Justice Throne of Geth Unbounded Potential Vat Emergence Volt Charge Vraska, Betrayal's Sting Wanderer's Strike Whisper of the Dross Yawgmoth, Thran Physician Yawgmoth, Thran Physician

Smokestack has the following oracle text: At the beginning of your upkeep, you may put a soot counter on Smokestack

First, it was foils, introduced back in Urza's Legacy