At the end of 1-2, get on the pipe and break 2 blocks so there is 1 touching the pipe. Duck and jump into the block (this will take practice). If this is done right, you will be sucked into the wall. If you go too far this will not work. Go into the pipe that leads to world 4. You will be in World -1. It is a endless water level(for example if you went through the pipe at the end you will go back to the beginning of the water level).
Fire Power Skate:
When you come out of a pipe,(Fire Power Required)hold A and B. If done right, you will jump when you come out of the pipe. Let go of A and you will skate for about 5 seconds.
This cheat works well at 1-2. When you have fire power, go into the pipe and hold A and B. When you get outside, you will jump. Let go of A and you will skate. QUICKLY get hit by the plant and you will skate while small.