The Old Windmill
Do not collect the key below the windmill till last. There's a teleporter in in windmill.
Use Stinky to push the boulder (red X) along the light blue path and leave it at the dark blue X. Now go throug the windmill and move quickly along the yellow path. Use Loof to push the boulder along the light blue path. Push the boulders on the dark blue and yellow X up. Use Stinky to move along the red path and push the boulder through the teleporter. Make Loof push the boulder to the dark blue X. Move Stinky along the white path and onto the white X. Move Loof through the teleporter and along the purple path. Boulders should now be positioned at the purple circles. Use Loof to push the rightmost of these to the right and the boulder on the yellow circle down. Place Loof on the light blue X. Move Stinky down pushing the boulder and position him 2 squares above the teleporter without disturbing any other boulders. Make Loof push the bottom boulder right and the boulder above the ice right. Make Stinky push the boulder down and along the light blue path to the yellow X. Push the boulders on the dark blue and yellow X up. The remaining two boulders can now be pushed through the teleporter, along the light blue path and up from the dark blue X. Use the metal boxes hidden in the wall (green X) to complete the bridge. Use Loof to collect the key behind the windmill. Collect remaining keys and bonus coins and exit.