Where can I find the star coin for W5-2?

In the room with the spinning spikes there is a hidden ledge. Jump at the wall at the bottom of the screen and you should find it.

You need to be Fire Mario. In the room with the spining spikes take the path on the other side from which you enter. Youll get to a room with four torches and an iron gate. If you lit the torches youll hear a familiar sound and the gate opens up. Behind it youll find the star coin your searching for.

When you get to a circular room jump up the platform south and you will find this.

Hope this helps