Historical Rules · 23 April 2010
Rule 103.4c
Official source text from the 23 April 2010 Rules release
The Two-Headed Giant variant uses the multiplayer mulligan rule, with a slight modification. First, each player on the starting team declares whether or not he or she will take a mulligan. Then the players on each other team in turn order do the same. Then all mulligans are taken at the same time. A player may take a mulligan even after his or her teammate has decided to keep his or her opening hand.