The Countdown Is at One is a rare Sorcery card from Unstable (UST), collector number 80. Current market price: $0.26 (foil $0.35), TCGplayer market prices via Scryfall.
Players play a Magic subgame, starting at 1 life and using their libraries as their decks. For the rest of the main game, if a source would deal damage to a player who didn't win the subgame, it deals double that damage to that player instead.