World 5: Mid Castle

Coin 1 (before checkpoint)

You'll find the first Star Coin in the third moving section of the shaft, just before the checkpoint. Look for it on the right once the wall recedes enough to reveal it.

Coin 2 (after checkpoint)

Shortly after the checkpoint, the shaft will split into two--jump up the left one quickly to grab the Star Coin while it's exposed from the receding wall.

Coin 3 (after checkpoint)

You'll find the final Star Coin at the very top of the shaft, just right of the boss door. Follow the gap in the moving wall and bust the blocks whenever you get the chance until you can reach the Star Coin.