Scrap Trawler

The single restriction (return an artifact of strictly lesser mana value) is what turns this into a descending staircase rather than an infinite loop. Sacrifice a four-drop and reclaim a three; sacrifice the three and reclaim a two; sacrifice the two and reclaim a one. Each step down is mandatory in direction but free in execution, and the cascade self-terminates when you run out of cheaper targets. Because the trigger fires whenever any artifact you control dies (the construct's own death included), it counts itself: the last link in any chain can be the Trawler, returning one final lower-value artifact on its way out. That self-inclusion is the wrinkle that makes it more engine than payoff. The cost restriction also dictates how you build around it: a curve of stepped mana values, not one expensive bomb, because every artifact needs a smaller one waiting underneath to catch the return. Zero-cost artifacts are the floor, not the fuel; nothing is cheaper than they are, so cashing one in returns nothing, and they exist only to be the bottom rung something else lands on. This is what artifact-aggregation decks had been missing: a way to keep small pieces circulating rather than spending them once. The 3/2 body is incidental. What you are buying is a value-conversion piece dressed as a creature, the glue that makes a pile of cheap artifacts behave like a machine.