In filler your goal is simple: fill 2 / 3 of the level. To create a filler ball, press down. It grows, until you release the mouse button, there is an other filler ball or a bouncing ball into runs.

Mouse down to create a filler ball. You have to the mouse, it freezing. You have a limited number of life and every level balls. If you a bouncing ball squash, it again is displayed in the upper right corner.