From the Super Mario Wiki
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The level features six Mini Toads.
The stage is a high-rise of gray girders with Red Girder Rivets attached to them. Two pairs of Split Pipes, one yellow and one red, lead from the bottom to the top on each side of the course. One pair of Mini Toads starts on different platforms on one side, another starts in a similar formation on the other side, and the third pair is located under the Goal Door on the middle line.
The ground under the Goal Door consists of a Red Girder platform, the only one initially present in the stage. Throughout the stage, the Minis must gradually collect Girder Pickups so that they acquire enough Red Girders to traverse the floors and reach the goal.