First you take a barrel (those big things you hit to get coins) and hit it against a wall. Then hit it slowly until it is just past the wall. After that you change into your blob form and jump on top of the barrel until you are pressing against the wall, you may fall down at first then come back up, that means that the glitch may not work and you should restart. You should be shaking very slightly now. That is OK though. Now switch to your main character form and jump and press in the direction of the wall while changing. You should end up jumping through the wall when you finish changing. You can then land in small tunnels that only blobs should be able to get into as you main form or land in another room. This glitch wears off when you touch ground in a room. To get out of the small tunnels turn into your blob.