New Super Mario Bros. Wii 5-Castle QSC

The 1st Star Coin is past the first set of circular grates. I got it using the Propeller Suit, but you can also get it by wall-jumping. The 2nd Star Coin is in a room hidden up in the ceiling by the circular grate to the right of the 1st Star Coin. Climb up the left side to find a hidden door. There are several Podoboos jumping out of the lava and the Star Coin is just under the door. Grates appear out of the lava periodically, so you can give yourself a boost when trying to jump for it. The 3rd Star Coin is after the 4 vertically moving grates on the main level. I waited until the 4th one was at its peak, then jumped and clung to the 5th one rising out of the lava. This can be difficult to get.