Instructions
Go through the level until you pass two silver pipes and come across your second pool of lava.
Locate the moving platform in the lava. This can be difficult to see since the two are colored similarly. Jump on it when it is near you. Jump to the stone on the opposite side of the pool when you approach it.
Approach the first silver pipe and wait for the plant head to sink back inside. Jump on the pipe and press "Down" to travel down it, taking you to another part of the level.
Walk past the three pipes and jump over the lava pool. There will be a silver pipe in mid-air.
Jump two blocks before the pipe to reveal a hidden block. Jump on the hidden block and wait for the plant head to sink. Jump on the pipe and press "Down" to go to another part of the level.
Walk past two silver pipes and jump across another pool of lava. Jump onto the next silver pipe -- third from where you arrived -- and press "Down."
Swim across the level, taking care to avoid the spinning fire rods and bloopers. Press "Right" as you approach the green pipe.
Pass the silver pipe, taking care to avoid the hammer brother. To make the jump across the following pool of lava easier, you may want to defeat the enemy. Either shoot fireballs at him or jump on his head.
Approach the lava pool and wait for the fireball to jump up and back down again. Hold down "B" to run and jump across the pool.
Avoid Bowser's projectiles and defeat him. You can either shoot fireballs at him or hit the ax, releasing the bridge beneath him. Run beneath Bowser as he jumps or jump over him yourself to hit the ax.