From the Super Mario Wiki
Flopside Tower is a tall, dark building situated in the center of Flopside. Like the Flipside Tower, it is the highest accessible floor in the town, and jumping off of it serves as a shortcut to the third floor. However, unlike its Flipside counterpart, it is only accessible via an elevator located on the second floor, whereas the Flipside Tower is accessible via an elevator on the second floor of Flipside, or by using the Return Pipe. However, if the player uses the Return Pipe in Castle Bleck, they will be taken to the Flopside Tower instead.
The Flopside Tower acts as the Flopside equivalent to the Flipside Tower. As a result, it has a very similar function. However, unlike the Flipside tower, which allows access to seven different dimensions, the Flopside Tower only allows access to the last dimension in the game, Castle Bleck.
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