BoxBoy! + BoxGirl!
Like previous entries in the series, BoxBoy! + BoxGirl! is a puzzle platform video game. The main gameplay mechanic revolves around generating a chain of boxes to overcome obstacles and reach the end of the level. Each level has a limit on the number of boxes that can be created at a time. Boxes can be used for a variety of functions, such as forming bridges, blocking hazards, and pressing switches. In the single-player campaign, dubbed "A Tale for One", players control Qbby to create strings of boxes which can be placed down, held out, or retracted by Qbby. Levels are grouped into worlds, each of which are themed with different obstacles and abilities.
BoxBoy! + BoxGirl! contains 270 levels across three campaigns, the most of any game in the series. For the first time in the series, the game features a two-player campaign, "A Tale for Two". In this mode, one player controls Qbby and the other controls Qucy, and both work together to progress their way through the levels. Each level has a limit on the number of boxes that each player can create at a time. Puzzles in the two-player campaign often require cooperation between the players to be solved. The two-player campaign can also be played individually by switching back and forth between controlling Qbby and Qucy.
A third campaign can be unlocked, "A Tall Tale", in which players control Qudy, a rectangular character that can rotate horizontally and vertically. This campaign features an extra set of puzzles that take advantage of the long, rectangular-shaped boxes that Qudy can create.
The levels feature collectible crowns which reward players with medals, which can be used to buy bonuses such as cosmetics, power-ups, and challenge stages. Medals can also be obtained by completing a level using a limited number of boxes. The in-game currency can also be used to buy hints that demonstrate how to complete the level.