Hedron Crab

The card that turned mill from a slow novelty into a real clock. The trick is that landfall fires on every land entering, not just lands played for turn, so the engine scales with the deck around it: fetchlands double the trigger, extra-land effects multiply it, and a single turn can bury nine or twelve cards instead of three. The 0/2 body is the giveaway that this was never built to attack; it is just enough toughness to stick under the cheapest sweepers and ping effects while the lands do the actual work, and cheap enough that losing it to a burn spell costs the opponent a card to stop something that already triggered. The trigger targets a player, so it can grind one library or split across a table, but the real design statement is the conversion of a resource every blue deck already plays (lands) into incremental graveyard damage at no extra mana. That linkage is why it remained the anchor of dedicated mill long after flashier finishers came and went: it asks nothing you were not already doing, and it rewards every fetch and ramp piece you would have run anyway. Most mill cards are payoffs that need a critical mass to matter. This one is the engine that builds the critical mass, one land drop at a time.