Explanation: If you hop into the spin-formation and walk towards the wall and the save block, the game will slightly clip you into the wall. Behind the inbounds wall that is only a few pixels thin, is another kind of wall (I call it the OoB wall since that kind of wall only appers in Out of Bounds areas) that allows you to clip through pretty easily. By "wiggling" the pad towards the OoB wall, it should clip you through at one point. Once you are through the first OoB wall, just walk up and you get to the second OoB wall. Just "wiggle" through it. Now head to the top and complete the Dreamy Somnom Woods.

                After you completed the Dreamy Somnom Woods, you come to a problem. The track is not there.
                LUCKILY there is this one ?-block just in the perfect position to clip you OoB.
                The trick about that clip it to hop into the spin-formation just above the ?-block, and then hold straight down.
                If done correctly, you should be just a bit in the wall. Now don't jump of Luigi immediately and just walk a bit to the left.
                Now you should be OoB and you can just walk to the beginning. The best spot do get back inbounds is at the statue.

IMPORTANT: DON'T get into any of the pathes that the track would send you to or you will be stuck!

Time saved: about 20 minutes