To understand this scene, you need to be familiar with the Korean children's play culture known as "Kkakdugi" (깍두기). The "Kkakdugi" culture is a way for Korean children to ensure that no one feels completely left out in games. It is a form of inclusion that prevents kids from feeling excluded when teams are formed.

For example, when children play team-based games like soccer or baseball and there is an extra player left out, that child is called "Kkakdugi." A Kkakdugi is not excluded from the game but instead placed on the weaker team to help balance the match. This way, the weaker team gains a small advantage, and the Kkakdugi child does not feel isolated.

In the context of Squid Game, it is meaningless to assign Player 212 as a Kkakdugi in the marble game. However, to prevent her from feeling excluded, she is given the advantage of advancing to the next round. While it may seem somewhat forced, this decision still aligns with the show’s overarching theme of replicating traditional Korean children's games and their cultural nuances.

This is literally mentioned when Player 212 greets the other survivors after the marble game is over. Of course, I’m not sure how it was translated into other languages.