OK, this bug is kinda hard, but very useful, (beat first Koba (or whatever) and get to last one).

1. when you got the first key, go into the next area, and go to the stairs to the next door.

2. stand with your back to the door at the end of the stairs (down), then use the forward jump and quickly (while in the first jump) start to go backwards while clicking the jump button (NOTICE: remember to hold the other button to use the forward jump)

3. if you did this right, you will go backwards WHILE doing the forward jump (but its called Backwards jump from now on)

4. if you press the jump button fast enough, you will gain so much speed, that you will smash through the door and you will enter the next area (if you hit the wall, you will be stuck in the wall for a few seconds)

5. now, go up the stairs, and do the same. This place is much easier because you can't reach the top of the stair, and when you start to gain the speed, you will suddenly see the top and maybe you will get pushed down into the hole.

6. go and beat Boser (or whatever) silly with your 20 stars or whatever you need ^^