Grindclock

A mill engine that starts at zero and has to be wound up before it threatens anyone. The two abilities share a single tap, and that is the whole design tension: one activation charges, one mills, and you only get one per turn. Crucially, milling does not consume the counters. It reads how many are sitting on the artifact and mills that many, leaving the count intact for next time. So the output is a ratchet that only climbs. Tick to one and you can mill one every turn thereafter; tick to two and you can mill two; keep alternating and the figure compounds toward a number that empties a library in a single activation. The catch is that every turn spent charging is a turn spent doing nothing visible, and that ramp is the engine's exposure. A fast clock ends the game long before the counter total matters, and a single removal spell erases every banked turn of investment at once. What it actually wants is a board that has ground to a standstill, where nobody can punish the early turns it spends winding up. This belongs in the patient, inevitable corner of mill, closer to a siege weapon you assemble over many turns than to a burst spell that dumps a library in one swing. The payoff arrives later than it feels like it should, because the count only ever rises by one per charge. Survive long enough behind a locked board, though, and it does not chip at a library: it deletes one.