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600.4. Unlike two-player games, multiplayer games can continue after one or more players have left the game.
600.4a. When a player leaves the game, all objects (see rule 200.8) owned by that player leave the game, all spells and abilities controlled by that player on the stack cease to exist, and any change-of-control effects which give that player control of any objects end. Then, if there are any objects still controlled by that player, those objects leave the game. (Any objects leaving the game this way that aren’t owned by the player leaving the game are placed in the removed-from-the-game zone.) This is not a state-based effect. It happens as soon as the player leaves the game. A player leaving the game doesn’t affect combat damage on the stack.
600.4b. If an object would change to the control of a player who has left the game, that object’s control remains unchanged. If a token would be put into play under the control of a player who has left the game, no token is created.
600.4c If an object owned by a player who has left the game would be put into any zone, it leaves the game instead. (This includes abilities that would be put onto the stack.)
600.4d If an object requires a player who has left the game to make a choice, the controller of the object chooses another player to make that choice. If the original choice was to be made by an opponent of the controller of the object, that player chooses another opponent if possible.
601.1. Limited range of influence is an option that can be applied to most multiplayer games. It’s always used in the Emperor variant (see rule 607), and it’s often used for games involving five or more players.
601.2. A player’s range of influence is the maximum distance from that player, measured in player seats, that the player can affect. Players within that many seats of the player are within that player’s range of influence. Objects controlled by players within a player’s range of influence are also within that player’s range of influence. Range of influence covers spells, abilities, effects, damage dealing, attacking, and making choices.
601.2a The most commonly chosen limited ranges of influence are 1 seat and 2 seats. Different players may have different ranges of influence.
601.2b A player is always within his or her own range of influence.
601.2c The particular players within each player’s range of influence are determined as each turn begins.
601.2d An object is within a player’s range of influence if it’s controlled by that player or by another player within that many seats of that player.
601.3. Creatures can attack only opponents within their controller’s range of influence. If no opponents are within a player’s range of influence, creatures that player controls can’t attack.