Drag, and the whole board shifts one cell — not as far as it can go. Two equal numbers double only when the tile in front has nowhere left to move, so every merge is one you set up.
Nothing is random. The tiles come off a written deck you can count, and the next three are already on screen, so a jam two moves away is one you can see coming.
Four decks: plain numbers, stones that block until you crack them, a wild that takes any value, and a board that grows with your biggest tile.