Historical Rules · 16 July 2010
Rule 810.10
Official source text from the 16 July 2010 Rules release
The Two-Headed Giant variant can also be played with equally sized teams of more than two players. Each team's starting life total is equal to 15 times the number of players on the team. (These variants are unofficially called Three-Headed Giant, Four-Headed Giant, and so on.)