Battered Golem

The defect is the design. A creature that can't untap on its own is dead weight in any deck that wants to attack twice, so the body comes pre-broken and the artifact trigger is the patch: every artifact entering the battlefield offers to stand the Golem back up. In an artifact-dense shell that means it can attack or block, then untap as you advance your board and be ready to repeat next turn. The trigger only ever untaps the Golem itself, though, which is both the line that keeps it honest and the limit on its reach. It is not a universal untap node for your other permanents. To turn it into a repeatable engine you have to route value through the creature: pair it with Springleaf Drum, which taps a creature as a cost, or an equipment that grants a tap ability, so that "untap the Golem" quietly becomes "fire that ability again." That indirection is the whole character of the card. A slow 3/2 with a self-imposed handicap when nothing else is happening; surrounded by artifacts hitting the battlefield every turn it becomes a body that refuses to stay tapped and, with the right tap-cost outlet bolted on, an early experiment in untap-as-resource. The card has no contribution to make in a deck that isn't routing artifacts onto the battlefield, and a real one in a deck that is.