Secret Limerick
From Glitches
From the game A Boy and His Blob for the NES.
There's a way to place holes in the floor so that you can fall and run right through walls. This can be used to either skip whole areas or run through parts of the game that don't exist during normal gameplay (scrambled screens, the credits screen, the ending scene, and even one that contains 5/6ths of an unused limerick).
