Voltaic Servant

An untap engine wearing the body of a blocker. The end-step trigger is the quiet half of the design: it fires after combat, after your spells, after the turn's permissions are mostly spent, which means the artifact you untap is reset and ready for whatever happens on the opponent's turn rather than being pre-spent on yours. That timing turns it into a free second activation of any tap-to-do-something artifact: a mana rock that taps twice across the turn cycle, a tapper that holds a creature back on defense, a charge-counter machine that ticks a step faster. The 1/3 frame is doing real structural work alongside the trigger; it survives the early aggressive turns where you most want the untap loop running, and it asks for nothing in return except an artifact worth pointing at. It does not loop on its own, which is the line that keeps it fair: the target is chosen each end step, so the payoff scales precisely with how many tap abilities you have stacked around it. In artifact-dense shells it is glue, the cheap construct that makes every other rock and engine count for one and a half. Outside them it is a 1/3 that stares at nothing useful and untaps itself most turns.