Instructions
Enter World 1's tower while you have the Blue Koopa Shell power-up. This power-up can be found throughout the levels or mushroom hut prior to the tower, and it will allow Mario to withdraw into a protective shell. Just past the halfway point you will see a green pipe which will launch you upward and a gold door nearby. Go through the door into a room with the second star coin and moving blocks. Go to the upper-right of the room and move right through the wall. Use the Blue Shell ability to break the three blocks and go past them through a red pipe to finish the level. You can then go to the first warp cannon which leads to World 5.
Unlock level 2-A by going through the alternate exit in level 2-3. In the second part of the level swim through an opening in the ceiling to find a coin room. Hit the switch in the room to raise the water level and leave through the top of the room. Finish the level to unlock 2-A.
Go through the yellow pipe at the end of the first part of level 2-A. Reach the pipe by jumping off the final spinning platform to reach the last star coin then falling to the right side of the screen. Land on the red Koopa and press the jump button at the same time to reach the pipe. Go through it to finish the level and reach the World 5 warp cannon.
Enter the World 3 ghost house and go as far right as you can. Hit the orange switch and go back to the left and hit the previous switch. Go through the door that appears after hitting both to finish the level and gain access to the World 6 warp cannon.
Go into the World 4 ghost house and go as far to the right as you can. Enter the door and hit the switch on the left. Go to the right and jump on top of the pipe but do not enter it. Wall jump off the wall to the right and enter the door to finish the level and get the World 7 warp cannon.
Unlock the World 8 warp cannon by going to the World 5 ghost house alternate exit. When you reach the first door, jump on the three blocks above it to reveal hidden coin blocks and a beanstalk. Climb it and let the boxing boo destroy all the blocks in the next room. Go through the door and jump on the platform that begins to rise. Once you're at the top go through the door and finish the level to unlock the World 8 warp cannon.