Historical Rules · 23 January 2015
Rule 715.2
Official source text from the 23 January 2015 Rules release
As the subgame starts, an entirely new set of game zones is created. Each player takes all the cards in his or her main-game library, moves them to his or her subgame library, and shuffles them. No other cards in a main-game zone are moved to their corresponding subgame zone, except as specified in rules 715.2a–d. Randomly determine which player goes first. The subgame proceeds like a normal game, following all other rules in rule 103, “Starting the Game.”