Filler 2 is a simple time-waster. You click and hold the mouse to start creating a bubble. While your bubble inflates, it may not touch any of the red bubbles that are floating around the screen. As soon as you let go of the mouse button, your bubble becomes solid and floats down the screen; the red bubbles can no longer harm it.
Your goal is to fill two-thirds of the screen space with your bubbles. You can only make so many bubbles before you strike out. You’re allowed to make more and more bubbles on each new level (so they can be smaller), but there are more and more red bubbles floating around the screen, too (so you have to make your bubbles smaller).
If all of this sounds a bit too soothing, there are also challenges that you can take. There are five challenge types: timed challenges (where you need to complete a level before the timer runs out), bubble-size challenges (where you must make a bubble of a certain size), perfection challenges (where you must finish the level without popping any balls), and quantity challenges (where you get fewer bubbles than normal to finish a level). There’s also a “meta” challenge mode, where “everything is a challenge.” I failed horribly with any and all challenges; they’re simply too tough for me. I like the normal mode, though. It’s kind of soothing, and that’s just the way I like my time-wasters.