Here is yet another hidden glitch. Enjoy!
sent in by Rick (Lickichu)
In level 1-2, go to the warpstar, but don't touch it!!!! Instead, go to the left until it is just out of sight. (Like one step off the screen with the warpstar) If you're lucky, the warpstar will be gone and you will be in a secret area with star blocks in the shape of HAL.