Arcum's Sleigh

Pile gate upon gate and you get an artifact that can almost never fire. The vigilance grant is mundane, but the conditions around it are an obstacle course: only during combat, only at the cost of a fresh activation each turn, and (the clause that breaks it) only if the defending player happens to control a snow land. The central restriction points at your opponent's mana base rather than your own, so the engine depends on a board state you have no way to guarantee. Ice Age built its snow theme on the assumption that snow-covered lands would be a common deckbuilding choice; they were not, and so a card written to exploit them found nothing to exploit. The result is a piece of tech engineered to punish a decision the format never forced anyone to make, and it sits at the far edge of how much conditional text a card can carry before it stops working at all. What survives is the design as artifact: a record of Wizards testing the ceiling on "matters" clauses during a period when the rules vocabulary was still being invented, with Arcum's Sleigh marking exactly where the experiment overshot.