General Rulings - 421

• 421.1 - Occasionally the game can get into a state in which a set of actions could be repeated forever. These rules (sometimes called the "infinity rules") govern how to break such loops. [CompRules 2003/07/01]
• 421.2 - If the loop contains one or more optional actions and one player controls them all, that player chooses a number. The loop is treated as repeating that many times or until another player intervenes, whichever comes first. [CompRules 2005/08/01]
• 421.3 - If a loop contains optional actions controlled by two players and actions by both of those players are required to continue the loop, the active player (or if the active involved is not involved, the first involved player after theactive player in turn order) chooses a number. The other player then has two choices. He or she can choose a lower number, in which case the loop continues that number of times plus whatever fraction is necessary for the first player to "have the last word." Or he or she can agree to the number the first player chose, in which case the loop continues that number of times plus whatever fraction is necessary for the second player to "have the last word." (Note that either fraction may be zero.) This sequence of choices is extended to all applicable players if there are more than two players involved. [CompRules 2008/10/01]
  Example: In a two-player game, one player controls a creature with the ability "{0}: [This creature] gains flying," and another player controls a permanent with the ability "{0}: Target creature loses flying." The "infinity rule" ensures that regardless of which player initiated the gain/lose flying ability, the nonactive player will always have the final choice and therefore be able to determine whether the creature has flying. (Note that this assumes that the first player attempted to give the creature flying at least once.) [CompRules 2005/08/01]
• 421.4 - If the loop contains only mandatory actions, the game ends in a draw. (See Rule 102.4b.) [CompRules 2006/02/01]
• 421.5 - If the loop contains more than one set of optional, independent actions each controlled by different players, and the active player (or, if the active player is not involved, the first involved player after the active player in turn order) chooses a number for his or her set of actions. Knowing that number, the remaining players, in turn order, each choose a number for his or her sets of actions. It can be higher, lower, or the same. Then each set of actions occurs the appropriate number of times. [CompRules 2008/10/01]
• 421.6 - If the loop contains an effect that says "[X] unless [Y]," where [X] and [Y] are each actions, no player can be forced to perform [Y] to break the loop. If no player chooses to perform [Y], the loop will continue as though [X] were mandatory. [CompRules 2008/10/01]