World 7 - Level 2
The Library

First disable the "ring of fire" by position Stinky at the yellow "X" and - timing the pause in fireballs - following the yellow path. Now use four reflectors (two of each type) to build bridges at the green "X"s. Using the other four reflectors you can now - one at a time - destroy the two wooden boxes marked in light blue by releasing the cannon with the purple button. Use two more reflectors and the two leftover wooden boxes to build bridges at the light blue "X"s.
Now use Stinky, Loof, Qookie, and Peegue to press down all required buttons to reach the rainbow coins at the top of the level. You'll also need the two remaining reflectors and the boulder. To get the boulder onto one of the buttons use a reflector to stop it at the entrance of one of the middle rooms, then a bonus coin marked in purple to stop the boulder on the button - i.e. do not collect both purple bonus coins after that time.