Toadette finds herself in an area with Spikes and movable platforms. There are two arrow platforms to the side of the Spike in front of you. Touch them to move them in the direction of the arrows. This will make a path so the spike ball the Spike throws will roll into the gate in front of you and destroy it. Just be sure you're not standing directly on the other side of the gate. Once that gate is broken, move both arrow platforms, then rotate the camera so you can see the touchstone platform underneath where the gate was. Touch it to lower it so the Spike can destroy it. Move the closer arrow platform in front of you, stand on it, then move it so you can drop down to the hall. If you go around the corner away from the Spike, you'll find some coins. Walk around the corner where the Spike is and you'll find a couple of Piranha Sprouts. Pick one of them and walk to the railing and toss it at the first gem. The lone plant has multiple coins. Walk into the nearby corner and you'll find a plant with a key. Stand on the platform one of the Piranha Sprouts was on and touch it to lower it. You'll find a locked door and a Piranha Sprout around the corner. The door leads to the second gem. Return and move the arrow platform closest to the Spike on the opposite side of the gap to break the gate. Lower the platform at the end, carefully cross the spikes, then raise the platform. Cross the arrow platforms, moving them as necessary. An arrow platform in the corner has a plant with a Mushroom. Go around the corner and move the corner arrow platform behind the Spike for the third gem. Go back a short distance and use the arrow platforms to reach the arrow platform in the center. Move that one and time your drop onto the spikes below, then drop down to the floor. Stand on the touchstone to reveal a hidden Gold Mushroom, then get the Star.
Special Challenge: Find the hidden Gold Mushroom.