Cryptex

A two-mana rock that hides a card-advantage engine behind a commitment curve steep enough to reshape the deck around it. The mana it produces is a consolation prize; the real payload is the sacrifice mode, a surveil-three-into-draw-three that stays locked until the fifth unlock counter lands. Getting there is what the whole design turns on. Each counter demands you collect evidence 3, exiling three mana value worth of cards straight out of your graveyard, so five counters is fifteen mana value of self-mill and expendable fodder burned over the artifact's life. The graveyard is both the fuel and, once you finally draw three, part of what you refill, which is why the card wants a deck that churns its yard rather than hoards it. Build greedily and the artifact never opens; build around a graveyard that fills and empties as a matter of course and the payoff arrives as a byproduct of what the deck was already doing. Collect evidence is the mechanic that makes the loop legible, pricing each counter in graveyard material so the ramp and the draw are two ends of the same resource conversion. The deeper question the design poses is not whether the effect is good (surveil three then draw three, for no additional mana once the counters are set, plainly is) but whether a given game lasts long enough, and mills hard enough, to unlock it at all.