メンツが1人足りない

Missing, extremely new, or very obvious to obtain.

Based on the phrase “one person short.” It means a group needs, probably desperately, one more person to do something. In the chive’s case, the Lucky Snacks are in need of one more player for their Celestial Jade game. Maybe Qingque would play with them. The Chinese version, 三缺一, is a popular internet term used in the Mahjong game, which means that four players are needed to complete the game. If there are only three players, it is called "三缺一".