There is a cascade system in the game, which implies that symbols vanish after forming successful combinations to allow new icons to align. When this occurs, a growing multiplier is activated. This has a higher value during the bonus with free spins.
In the main game and the free spins bonus, the multiplier starts at 1x and 3x, respectively. In the regular game, it rises to 2x, 3x, and then 5x in repeated drops; during the free fall feature, it rises to 6x, 9x, and eventually 15x.