Number Mahjong is a tile-matching game that follows Mahjong rules. It features plain white tiles marked with black numbers and 100 unique layered tile patterns. The player must clear each level of all tiles. They also attempt to earn the highest score that they can in each level.
The game allows the player to select any pattern and level to start. Although it tracks the amount of time the player takes to remove a pattern entirely from the playfield, it doesn't have a countdown clock that causes the player to fail a level if they're not fast enough. Instead, it has a counter that shows the player's time for each level, which they can later use as a goal to beat when replaying the same level or removing patterns of tiles in other levels.
That said, the game does penalize the player score-wise for going too slowly. As each second passes and increases the number in the Time/Best area in the upper-right corner of the screen, the total score that appears at the start of the level decreases in the Score/Best area. If the player works too slowly, they can end a level with an incredibly low score. They also add seconds to the counter and reduce the score by hundreds of points if they choose to use the lower-right corner Hint button or Shuffle button.
The player can only remove uncovered tiles with at least one free left or right side that have the exact same numbers (i.e., 5 and 5, 10 and 10, 30 and 30, and so on). They can't remove covered ones or any tiles bracketed by other tiles on both sides.
