Magic: The Gathering -- Duels of the Planeswalkers

You're 20 into a game minutes and your next attack will secure you a win. There's just one more round of defense to survive, and you're confident you've got your opponent all wrapped up. His attack cards are all effectively blocked; no damage should be able to penetrate. But wait, what's this? Your wily adversary just dropped an Overrun card into play. Now all his attackers have increased damage and can spill their overkill numbers onto your life score. Which they do, and you die. Game over, so much for that.