World 3-Tower (New Super Mario Bros.)
From the Super Mario Wiki
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This level is a tower level that contains many fences and Climbing Koopas. To begin this level, Mario should jump into the middle Cannon Pipe, which will blast him into the air. Mario needs to grab onto the lowest metal fence, and then go to the left. Mario should jump onto the next fence, avoid the Climbing Koopas, and jump to get the first Star Coin. Then, using the Cannon Pipe again, Mario should grab the highest metal fence. Mario should flip the fence by punching the middle, and jump onto the next floor of the tower. The second Star Coin is obtained by going to the far left of the tower and jumping onto the metal fence above. The player can then go two ways: the left door, or the right door. The right door leads to the third Star Coin, and the left has another door that leads to coins, but both doors end up in the same place. Past the double doors is Bowser Jr.. To defeat Bowser Jr., Mario must jump on him three times and avoid his spiky shell.