Scrap Welder

The whole engine runs on a strict inequality: you sacrifice an artifact of mana value X and return one worth less than X, so every activation trades a bigger artifact for a smaller one. That downshift is the balancing gear. You cannot pull anything back for free (the returned artifact must cost at least one less than what you fed it), and mana value 0 fodder like Treasure or most tokens returns nothing at all, since there is no legal target below zero. What the ability wants is a heavy artifact you have already wrung value from, sacrificed to reanimate something cheaper you would rather have on the battlefield, with haste stapled on so it can swing or tap the turn it lands. That haste clause points the card at artifacts eager to act immediately, not parked engines. What keeps it from spinning freely is the tap and the need to keep supplying expensive fodder above the threshold, so it rewards a board where big artifacts are dying anyway rather than a static pile. It descends from a long line of red artifact recursion that treats the graveyard as a warehouse: Goblin Welder swapped artifacts in and out at will, and Daretti pushed the same impulse into the command zone. This is the taxed version of that idea, charging a mana value gap for each return instead of letting you cycle the same two artifacts endlessly.