Oracle Text:

Players must leave game in progress as it is and use the cards left in the libraries with which to play a subgame of Magic. When subgame is over, Players shuffle their cards, return them to their libraries, and resume game in progress, with any loser of subgame halving his or her remaining life points, rounding down. Effects that prevent damage may not be used to counter this loss of life. The subgame has no ante, using less then 40 cards may be necessary.