Shadowstorm

One red mana that does nothing the moment its quarry is off the table, and everything when the quarry is present. Shadow was Tempest's signature evasion: creatures fighting on a parallel plane, where ordinary blockers and most removal simply could not reach them. The whole pitch was that a board of cheap, fast attackers could win unopposed while the defender's creatures stood by, helpless. Removal was the only brake, and this is the brake built specifically for the job: a one-sided sweep priced to clear the small end of a shadow board for the cost of a single spell. The trade is total. Against shadow it is a blowout; against any other deck it is a blank, a card with no function outside its one intended target. That extreme is the tell of how the era handled pushed mechanics. Print the scary keyword, then print the cheap, narrow off-switch so the format has a known, color-appropriate answer on the books. The designer gets to push shadow hard precisely because this exists to punish a player who leans on it too heavily. The cost of that honesty is a card with zero life outside its matchup, which is exactly what the dedicated hoser is supposed to be: maximally efficient against one thing, maximally useless against everything else.