What occurs if an effect states that a player on a Two-Headed Giant team cannot lose life?

When an effect specifies that a player on a Two-Headed Giant team cannot lose life, it modifies the fundamental rules governing life loss for that team. In the Two-Headed Giant format, a team's life total is represented by the sum of the individual life totals of both players. If one player on the team is unable to lose life, it implies that the team itself effectively becomes immune to life loss as a unit for the duration of that effect.

This means that not only does the affected player not have to account for any life loss, but the entirety of the team cannot lose life either. Additionally, both players on that team are restricted from paying any life, as life loss is a direct consequence of paying life costs in many effects. Consequently, the correct understanding of this scenario is that the team collectively cannot have their life total decreased.

In context, the other choices provide incorrect interpretations of how life works in this scenario. For instance, stating that a team can lose a maximum of 10 life or regain life after losing it contradicts the concept of an effect preventing life loss entirely. Likewise, stating that the player must still pay life for other effects doesn't align with how effects mitigating life loss typically function.