New Super Mario Bros.: 6-Fort 2

This fort is filled will conveyor belts, many of which will send you into the spiked walls. The 1st Star Coin is over a conveyor belt to some spikes, which is to the right of two sets of spikes coming from the floor. Keep climbing and you'll reach the midpoint. There are some green pipes on the floor, which act as cannons. The left one will get you some coins. The right one will allow you to progress. You'll need to be at least Super Mario to break the bricks to the 2nd Star Coin. As you climb, you'll find a rope stretched across a gap. Use it to reach the 3rd Star Coin. The green pipe near the top of the fort is a cannon to the boss door. Bowser Jr.'s on the same kind of platform as in the last fort, but this time, he's wearing the mask. This means that you can't stomp him initially, as he'll immediately hide in his shell. He'll throw a Koopa shell at you, which you should stomp, then throw back at him. He'll flip on his back and you can stomp him then. Do this three times for victory. Fireballs work as well and are a much better way to battle him. He'll take Peach to the castle.