Rules

A free tile

Only a free tile can be taken. A tile is free when nothing rests on top of it and its left or right side is open. A tile squeezed between two neighbours is blocked even if the space above it is empty.

What counts as a pair

Two tiles match only when they are identical: the same number, the same wind, the same dragon. One does not match nine, east does not match south.

Layers

Tiles sit in several layers, each shifted a few pixels up and left. A tile in a higher layer hides what is under it, so the top is cleared before the middle and the middle before the bottom.

Why every board is solvable

Each layout is dealt backwards: first a removal order is chosen, then the tiles are labelled along it. A solution therefore exists by construction, not by luck.

Hint and shuffle

Hint lights up a pair that can be taken and costs ten seconds. Shuffle re-deals the tiles that are left; the new arrangement is solvable as well.