103.4b In a multiplayer game, the first time a player takes a mulligan, he or she draws a new hand
of as many cards as he or she had before. Subsequent hands decrease by one card as normal.
103.4d The Commander casual variant uses an alternate mulligan rule. Each time a player takes a
mulligan, rather than shuffling his or her entire hand of cards into his or her library, that player
exiles any number of cards from his or her hand. Then the player draws a number of cards equal
to one less than the number of cards he or she exiled this way. Once a player keeps an opening
hand, that player shuffles all cards he or she exiled this way into his or her library.