Since we've had a fair amount of players mention getting stuck on level 28 (the level with 3 stars at the top of the screen, with the black hole in the top left and the white hole in the top right), we wanted to provide a basic guide for how to finish the level. If you'd rather solve it on your own, DON'T LOOK FURTHER!
1. Go towards the larger platform on the left side near the black hole. Use the black hole to tip the star onto the platform and collect it.
2. Lower the black hole out of the top left corner (there is a gap), and make a hole in the wall blocking you from the middle of the screen. Jump into the middle area, then repeat to get to the right side of the screen.
3. Use the black hole to create a hole for the star in the top right to drop through, with you in position to catch it.
4. With the black and white hole now both available, you should be able to collect the final star by covering the center hole with the white hole and using the black hole to drop the star.