Defeat a God was one of the three "Horde Decks" created by Wizards during the original Theros block. It was designed for groups of players to play with sealed decks, and was likely inspired by the fan-created Zombie Horde EDH format. It's a cooperative format where a team of players faces down a deck that runs itself. The game works exactly as a normal game, except for these rules:
Here is the list of all of the Defeat A God cards.