Clock of Omens

Untap effects usually anchor mana-rock loops, but this one converts taps into taps rather than mana into mana, and that distinction is the whole engine. The cost is paid in other artifacts' tap states, which means anything with a useful tap ability that wants to fire more than once a turn suddenly can: a colorless mana rock, a card-drawing widget, a tap-to-activate toolbox piece, whatever wants its ability twice. The catch is the rate of exchange. Two untapped artifacts buy one untap, so the engine only nets value when the target produces more than two artifacts' worth of work per cycle, or when the two artifacts you tapped were going to sit idle anyway. That arithmetic pushes it toward boards full of cheap artifact creatures and zero-cost trinkets that exist purely as tapping fodder, the kind of dense artifact battlefield where two bodies are cheaper than the resource you free up. Built right, it spirals: untap the rock to pay for the next activation, untap a second engine, loop until you run out of fodder or land on something infinite. Built casually, it is a slow toy that asks for more pieces than it pays back. The line between those two outcomes is entirely a question of how many artifacts are already on the table, which is why it has never been a generically good card and always a payoff for one specific kind of deck.