810.5 With the exception of life total and poison counters, a team’s resources (cards in hand, mana, and so on) are not shared in the Two-Headed Giant variant. Teammates may review each other’s hands and discuss strategies at any time. Teammates can’t manipulate each other’s cards or permanents.
810.8 The Two-Headed Giant variant uses the normal rules for winning or losing the game (see rule 104), with the following additions and specifications.
810.8a Players win and lose the game only as a team, not as individuals. If either player on a team loses the game, the team loses the game. If either player on a team wins the game, the entire team wins the game. If an effect says that a player can’t win the game, that player’s team can’t win the game. If an effect says that a player can’t lose the game, that player’s team can’t lose the game.
810.9b If a cost or effect allows both members of a team to pay life simultaneously, the total amount of life they pay may not exceed their team’s life total. (Players can always pay 0 life.)
810.9c If an effect sets a single player’s life total to a specific number, the player gains or loses the necessary amount of life to end up with the new total. The team’s life total is adjusted by the amount of life that player gained or lost.
810.9d If an effect would set the life total of each player on a team to a number, that team chooses one of its members. On that team, only that player is affected.
810.9f If an effect instructs a player to redistribute any number of players’ life totals, that player may not affect more than one member of each team this way.
810.10a If an effect needs to know how many poison counters an individual player has, that effect uses the number of poison counters that player’s team has. If an effect needs to know how many poison counters a player’s opponents have, that effect uses the number of poison counters opposing teams have.
810.10d If a rule or effect needs to know what kinds of counters an individual player has, that effect uses the kinds of counters that player has and the kinds of counters that player’s team has. A player is “poisoned” if that player’s team has one or more poison counters.
810.11 The Two-Headed Giant variant can also be played with equally sized teams of more than two players. For each player a team has beyond the second, that team’s starting life total is increased by 15 and the number of poison counters required for the team to lose is increased by five. (These variants are called Three-Headed Giant, Four-Headed Giant, and so on.)