Swap two neighbouring tiles to line up three. Three of a kind is a pung; three tiles of one suit in sequence is a run, such as 4-5-6 bam. Cleared tiles leave gaps and everything above drops down, so one good swap can set off a chain.
Mahjong Cascade is a swap-to-match puzzle played with real American mahjong tiles. Move a tile one step up, down, left or right by tapping it and then tapping its neighbour. When three tiles in a line make a legal group they clear, the tiles above fall into the gap, and the tiles that land may make a group of their own. Those chain reactions are where the points are.
The groups are the building blocks of every hand on the National Mah Jongg League card: a pung is three identical tiles, and a run is three tiles of the same suit in sequence. Jokers do what jokers do at the table — they stand in for the tile you are missing — and three flowers clear together. Reading a cascade board is the same scan you run over a rack when you are deciding what to keep and what to pass.
Each level gives you a target number of tiles to clear and a budget of swaps. There is no clock: take as long as you like, and a Hint or a Shuffle is always available. If no swap anywhere on the board would make a group, the board reshuffles itself rather than leaving you stuck. Eight levels, from a six-by-seven warm-up to a full eight-by-nine well, rated from one to three stars on the swaps you have left.