This is a series that I will be making and updating as often as I can. If you have any feedback, please give it!

Star coin #1:
You'll see it almost right after you go underground. Jump when the crystal platform beneath is at its highest, or wall jump off the small piece of right wall.

Star Coin #2:
Once on the first platform that can be moved by tilting the Wiimote, use it to get into the pipe on the top right. In the new room, don't grab any of the small coins. Instead, hit the brick block in the center of the room to make a P-switch appear. Step on the switch, then quickly run and jump up the new brick platforms to claim the Star Coin before the time runs out.

Star Coin #3:
Later on, you'll see it under a section of red pipe. Break through the blocks covering the green pipe right before it with a ground pound(you must have to be big; small Mario isn't strong enough). Through the pipe, activate the POW block in this room to make the last Star Coin fall into here.