When you begin the stage for this star, head to the arch and cross the bridge to the fork by the first Bully. Take the left path now and cross the next bridge, once again ignoring the Mr. I here. Wait for the lava to subside on the platform beyond, then jump to the sliding puzzle with Bowser’s face. You simply need to collect all eight Red Coins here, which are all on the sliding puzzle, making this one of the easiest Red Coins stars in the game.
The pieces of the puzzle might seem to move randomly, but they move in a set pattern. If a piece of the puzzle is shaking, quickly move off of it, as it will drop you into the lava underneath (you won’t move with it). After collecting all eight Red Coins, the star will spawn on the stone platform in the corner of the puzzle.