Rule 729.2 · Subgames
As the subgame starts, an entirely new set of game zones is created. Each player takes all the cards in their main-game library, moves them to their 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 729.2a–c. Randomly determine which player goes first. The subgame proceeds like a normal game, following all other rules in rule 103, “Starting the Game.”
Subrules
As a subgame begins, if one or more supplementary decks of nontraditional cards are being used, each player moves each of their supplementary decks from the main-game command zone to the subgame command zone and shuffles it. (Face-up nontraditional cards remain in the main-game command zone.)
As a subgame of a Vanguard game starts, each player moves their vanguard card from the main-game command zone to the subgame command zone.
As a subgame of a Commander game starts, each player moves their commander from the main-game command zone (if it’s there) to the subgame command zone.