Scramble

In my view this is the most annoying level. The flow of fireballs seems to be completely random, unlike the release of enemies in the other levels. The best way to tackle this is obviously to use the rocks as cover. This may not be enough though as fireballs may keep you stuck behind the rock until you crash into it. A good way to avoid being trapped is to move you ship as far forward as possible while behind the rocks. as soon as you are able to move over and ahead, do so. If you are trapped then just hold backwards and wait until a gap appears. It's fairly rare that you will be trapped behind a rock all the way from a forward position to the back of the screen and until the rock hits you so this tactic should make the level a lot more manageable.

Hope this helps, message me on here if you need and further help