What is the outcome if an effect states that a player on a Two-Headed Giant team cannot gain life?

The outcome that a player on a Two-Headed Giant team cannot gain life means that the restriction applies to the entire team rather than just the individual player. In the Two-Headed Giant format, each team consists of two players who share a life total and collective board state. Therefore, if an effect states that a player cannot gain life, this limitation impacts both players on that team, effectively preventing them from increasing their life total through life gain effects.

In this scenario, it is important to consider the mechanics of team play in Two-Headed Giant. Life gain restrictions are considered at the level of the team rather than at an individual player level, making it impossible for the entire team to gain life while that restriction is in place. Understanding the collaborative nature of the Two-Headed Giant format helps clarify why the entire team's life gain is affected rather than just one player.

This reinforces the idea that conditions placed on individual players in a team format can have broader implications, particularly when those conditions relate to fundamental game mechanics like gaining life.