Millstone

The original mill card, and the one that named the mechanic. Before there was a keyword, before "mill" was a verb in the rules text of dozens of cards, there was this artifact: pay two, tap, take two off the top of a target player's library. The math is famously slow (twenty-seven activations to grind through a fifty-three-card library, ignoring everything else happening in the game), and that slowness is the point. The card is a clock that asks you to survive long enough to finish it, which made it the centerpiece of a deckbuilding question rather than a deck on its own: what does a control shell look like when its win condition is the opponent's library instead of their life total? Every dedicated mill strategy since has been an answer to that question, and every faster mill effect printed afterward (Glimpse the Unthinkable, Maddening Cacophony, the payoffs built around Bruvac the Grandiloquent) has been measured against the baseline this artifact set. The mechanic itself was eventually keyworded and named for the card, which is the rare case of Magic's design vocabulary being shaped by a single piece of cardboard from its first year.