In a four player game who doesn't use their battlefield?

In a four-player game, the player who does not use their battlefield is the player taking the first turn, as specified by the rules for the specific mode of play:

• In FFA4 (War) (Rule 465.4.b): The player who is taking the first turn removes their battlefields, and they will not be used for that game.
• In 2v2 (Magma Chamber) (Rule 466.4.b): The player who is taking the first turn removes their battlefields, and they will not be used for that game.