Each player draws a number of cards equal to their starting hand size, which is normally seven. (Some effects can modify a player’s starting hand size.) A player who is dissatisfied with their initial hand may take a mulligan. First, the starting player declares whether they will take a mulligan. Then each other player in turn order does the same. Once each player has made a declaration, all players who decided to take mulligans do so at the same time. To take a mulligan, a player shuffles the cards in their hand back into their library, draws a new hand of cards equal to their starting hand size, then puts a number of those cards equal to the number of times that player has taken a mulligan on the bottom of their library in any order. Once a player chooses not to take a mulligan, the remaining cards become that player’s opening hand, and that player may not take any further mulligans. This process is then repeated until no player takes a mulligan. A player can take mulligans until their opening hand would be zero cards, after which they may not take further mulligans.
April 27, 2018 · Dominaria
Some cards allow a player to take actions with them from their opening hand. Once the mulligan process (see rule 103.4) is complete, the starting player may take any such actions in any order. Then each other player in turn order may do the same.
September 26, 2015 · Battle for Zendikar
Some cards allow a player to take actions with them from his or her opening hand. Once the mulligan process (see rule 103.4) is complete, the starting player may take any such actions in any order. Then each other player in turn order may do the same.
September 30, 2011 · Innistrad
Some cards allow a player to take actions with them from his or her opening hand. Once all players have kept their opening hands, the starting player may take any such actions in any order. Then each other player in turn order may do the same.
June 17, 2011 · Commander 2011
Some cards allow a player to take actions with them from his or her opening hand. Once all
May 1, 2011 · New Phyrexia
Some cards allow a player to take actions with them from his or her opening hand. Once all players have kept their opening hands, the starting player may take any such actions in any order. Then each other player in turn order may do the same.
April 1, 2011 · Duel Decks: Knights vs. Dragons
Once all players have kept their opening hands, if any cards in the starting player's hand allow that player to begin the game with those cards on the battlefield, he or she may put any or all of them onto the battlefield. Then each other player in turn order may do the same.
February 4, 2011 · Mirrodin Besieged
Once all players have kept their opening hands, if any cards in the starting player’s hand allow that player to begin the game with those cards on the battlefield, he or she may put any or all of them onto the battlefield. Then each other player in turn order may do the same.
October 1, 2010 · Scars of Mirrodin
Once all players have kept their opening hands, if any cards in the starting player’s hand allow
February 1, 2010 · Worldwake
Once all players have kept their opening hands, if any cards in the starting player's hand allow that player to begin the game with those cards on the battlefield, he or she may put any or all of them onto the battlefield. Then each other player in turn order may do the same.