World 4 - Level 7
Switch to Loof and enter the green teleporter from below (!), then move the Reflector to the yellow "X". Stand to its right. Switch to Stinky and step on the yellow button, this will destroy the two wooden boxes marked in yellow. Now have Loof move the Reflector to the green "X" and guide two fireballs to destroy the two wooden boxes marked in green. Careful, Stinky is right behind those boxes - make sure you don't shoot more than two fireballs. Switch to Stinky again and collect the two Rainbow Coins behind the red and yellow teleporters. Then place Stinky at the white "X".
Enter the blue teleporter with Loof and step on the purple button. Switch back to Stinky and let five fireballs destroy the five boxes marked in white (be sure to leave one box standing on the left side). Switch back to Loof and step off the purple button. Build a bridge with the remaining four boxes, and exit the level.