World 7 - Level 10
The first difficulty is to get safely to the bottom of the level.
To do so, build a bridge to the north and get three steel boxes into position at the yellow "X"s. Then push the box along the green arrow (just one step), and move to the green circle. Push the box along the blue arrow, and move to the blue circle. Now wait until a fireball has passed and move along the white path. Repeat this process until you are at the bottom.
Once you are at the above position, you have several choices. To just complete the level, run to the white spot and back several times to get the Flying Saucers to destroy each other. One might survive, but you can then use the central box as a shield, pushing it down and then toward the Flying Saucer. Collect the Rainbow Coins, and return to the safe spot between the two steel boxes. Wait until a fireball passes, and make a run for the exit.
If you do want to get all the Bonus Points, the matter is a lot more dangerous. You'll need at least one Saucer to survive on each (!) side. To do so, push the middle box down and run toward one side using it as a shield. use a side corridor as soon as possible to avoid the incoming fireballs behind you. Now use the box to disrupt their standard flight patterns, and trick them into destroying the wooden boxes for you. Collect the bonus points and switch to the other side.