New Super Mario Bros.: 3-Castle

This castle is filled with spike pillars. Duck under one of them for the first Star Coin. After the midpoint, you will encounter Whomps. They can be killed with a ground pound, but do not kill the one over the spikes: it keeps you from hitting them. To get the second Star Coin, go past it to the right and climb up the pole. Use the rope to swing over to it, making sure the Whomp is lying over the spikes. To the right are lots more spike pillars. You will reach the boss door, but can go under it into the water. To the right is another pillar and the third Star Coin. Get into the water, then climb up when the spike pillar retreats to get it. Through the boss door, we encounter a Giant Cheep-Cheep. It will swim around on the water below, then jump onto the bridge, bounce a few times, then return to the water. Jump on it three times to win, while avoiding the smaller Cheep-Cheep that jump up. Victory gives us the key, then Bowser Jr. carries Peach off to World 5.