From the Super Mario Wiki
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The player starts before a group of pillars with the first three having Fire Bars in them (the third Fire Bar being longer than the others), a Lava Bubble jumping up between the first two, and a ? Block with a power-up above the second pillar. Through a passage with a Fire Bar on the ceiling, the player will arrive at a large pit of lava with a Fire Bar before it and a Lava Bubble jumping up from the lava; to cross, the player has to time a jump off of the Fire Bar. After a narrow passage at the top of some stairs with a Koopa Troopa are narrow pillars the player has to jump between while avoiding Lava Bubbles. The player then has to pass through a narrow passage with Bill Blasters, two on the floor and one on the ceiling. By running and then jumping off of the third Bill Blaster, the player can cross the lava pit and reach the Fake Bowser, who throws hammers and breathes fire.