Goblin Welder

The engine that turned the graveyard into an artifact recursion loop before anyone had a name for it. The body is irrelevant; what matters is an activated ability that costs nothing but a tap and reads more like a free spell than a creature ability. The crucial design constraint is that both targets belong to the same player: the artifact card you return has to come from the graveyard of whoever controls the artifact you sacrifice. Point it at yourself and you weld a do-nothing rock away to bring something better up from the bin; point it across the table and the opponent sacrifices their good artifact to drag back a worse one. The "simultaneously sacrifices and returns" wording is what makes it abusable: both halves resolve on a single beat, so sacrifice triggers, enters-the-battlefield triggers, and leaves-the-battlefield triggers all fire off one tap each turn, and untap-step weld cycles compound across turns. That looped structure is why the card anchored an entire archetype, recurring payloads like Triskelion and Myr Battlesphere off the welds rather than off the mana it would cost to hardcast them, often fueling the loop by binning cheap artifacts you never meant to keep. It taps to do all this, dodging the cost line entirely, and the only real check is the 1/1 frame that any removal answers. A rare engine card whose power lives in the loops it enables rather than anything printed in its cost.